Multicomponent superabsorbent fibers

ABSTRACT

Multicomponent superabsorbent fibers are disclosed. The multicomponent fibers comprise at least one acidic water-absorbing resin and at least one basic water-absorbing resin. Each fiber contains at least one microdomain of the acidic resin in contact with, or in close proximity to, at least one microdomain of the basic resin. Blends of multicomponent superabsorbent fibers with particles of a second water-absorbing resin also are disclosed. Articles containing the multicomponent superabsorbent fibers also are disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part application of U.S. patentapplication Ser. No. 09/179,553, filed Oct. 28, 1998, pending, which isa continuation-in-part of U.S. patent application Ser. No. 09/120,674,filed Jul. 22, 1998, pending, which is a continuation-in-part of U.S.patent application Ser. No. 08/974,125, filed Nov. 19, 1997, pending.

FIELD OF THE INVENTION

[0002] The present invention relates to multicomponent superabsorbentparticles, in fiber form, containing at least one acidic water-absorbingresin and at least one basic water-absorbing resin. Each multicomponentsuperabsorbent fiber has at least one microdomain of the acidic resin incontact with, or in close proximity to, at least one microdomain of thebasic resin. The present invention also relates to mixtures containing(a) multicomponent superabsorbent fibers, and (b) particles of an acidicwater-absorbing resin, a basic water-absorbing resin, or a mixturethereof.

BACKGROUND OF THE INVENTION

[0003] Water-absorbing resins are widely used in sanitary goods,hygienic goods, wiping cloths, water-retaining agents, dehydratingagents, sludge coagulants, disposable towels and bath mats, disposabledoor mats, thickening agents, disposable litter mats for pets,condensation-preventing agents, and release control agents for variouschemicals. Water-absorbing resins are available in a variety of chemicalforms, including substituted and unsubstituted natural and syntheticpolymers, such as hydrolysis products of starch acrylonitrile graftpolymers, carboxymethylcellulose, crosslinked polyacrylates, sulfonatedpolystyrenes, hydrolyzed polyacrylamides, polyvinyl alcohols,polyethylene oxides, polyvinylpyrrolidones, and polyacrylonitriles.

[0004] Such water-absorbing resins are termed “superabsorbent polymers,”or SAPs, and typically are lightly crosslinked hydrophilic polymers.SAPs are generally discussed in Goldman et al. U.S. Pat. Nos. 5,669,894and 5,559,335, the disclosures of which are incorporated herein byreference. SAPs can differ in their chemical identity, but all SAPs arecapable of absorbing and retaining amounts of aqueous fluids equivalentto many times their own weight, even under moderate pressure. Forexample, SAPs can absorb one hundred times their own weight, or more, ofdistilled water. The ability to absorb aqueous fluids under a confiningpressure is an important requirement for an SAP used in a hygienicarticle, such as a diaper.

[0005] As used here and hereafter, the term “SAP particles” refers tosuperabsorbent polymer particles in the dry state, i.e., particlescontaining from no water up to an amount of water less than the weightof the particles. The terms “SAP gel” or “SAP hydrogel” refer to asuperabsorbent polymer in the hydrated state, i.e., particles that haveabsorbed at least their weight in water, and typically several timestheir weight in water. The SAP particles disclosed herein are in fiberform.

[0006] The dramatic swelling and absorbent properties of SAPs areattributed to (a) electrostatic repulsion between the charges along thepolymer chains, and (b) osmotic pressure of the counter ions. It isknown, however, that these absorption properties are drastically reducedin solutions containing electrolytes, such as saline, urine, and blood.The polymers function much less effectively in the presence of suchphysiologic fluids.

[0007] The decreased absorbency of electrolyte-containing liquids isillustrated by the absorption properties of a typical, commerciallyavailable SAP, i.e., sodium polyacrylate, in deionized water and in 0.9%by weight sodium chloride (NaCl) solution. The sodium polyacrylate canabsorb 146.2 grams (g) of deionized water per gram of SAP (g/g) at 0psi, 103.8 g of deionized water per gram of polymer at 0.28 psi, and34.3 g of deionized water per gram of polymer of 0.7 psi. In contrast,the same sodium polyacrylate is capable of absorbing only 43.5 g, 29.7g, and 24.8 g of 0.9% aqueous NaCl at 0 psi, 0.28 psi, and 0.7 psi,respectively. The absorption capacity of SAPs for body fluids, such asurine or menses, therefore, is dramatically lower than for deionizedwater because such fluids contain electrolytes. This dramatic decreasein absorption is termed “salt poisoning.”

[0008] The salt poisoning effect has been explained as follows.Water-absorption and water-retention characteristics of SAPs areattributed to the presence of ionizable functional groups in the polymerstructure. The ionizable groups typically are carboxyl groups, a highproportion of which are in the salt form when the polymer is dry, andwhich undergo dissociation and salvation upon contact with water. In thedissociated state, the polymer chain contains a plurality of functionalgroups having the same electric charge and, thus, repel one another.This electronic repulsion leads to expansion of the polymer structure,which, in turn, permits further absorption of water molecules. Polymerexpansion, however, is limited by the crosslinks in the polymerstructure, which are present in a sufficient number to preventsolubilization of the polymer.

[0009] It is theorized that the presence of a significant concentrationof electrolytes interferes with dissociation of the ionizable functionalgroups, and leads to the “salt poisoning” effect. Dissolved ions, suchas sodium and chloride ions, therefore, have two effects on SAP gels.The ions screen the polymer charges and the ions eliminate the osmoticimbalance due to the presence of counter ions inside and outside of thegel. The dissolved ions, therefore, effectively convert an ionic gelinto a nonionic gel, and swelling properties are lost.

[0010] The most commonly used SAP for absorbing electrolyte-containingliquids, such as urine, is neutralized polyacrylic acid, i.e.,containing at least 50%, and up to 100%, neutralized carboxyl groups.Neutralized polyacrylic acid, however, is susceptible to salt poisoning.Therefore, to provide an SAP that is less susceptible to salt poisoning,either an SAP different from neutralized polyacrylic acid must bedeveloped, or the neutralized polyacrylic acid must be modified ortreated to at least partially overcome the salt poisoning effect.

[0011] The removal of ions from electrolyte-containing solutions isoften accomplished using ion exchange resins. In this process,deionization is performed by contacting an electrolyte-containingsolution with two different types of ion exchange resins, i.e., an anionexchange resin and a cation exchange resin. The most common deionizationprocedure uses an acidic resin (i.e., cation exchange) and a basic resin(i.e., anion exchange). The two-step reaction for deionization isillustrated with respect to the desalinization of water as follows:

NaCl+R—SO₃H→R—SO₃Na+HCl HCl+R—N(CH₃)₃OH→R—N(CH₃)₃Cl+H₂O.

[0012] The acidic resin (R—SO₃H) removes the sodium ion; and the basicresin (R—N(CH₃)₃OH) removes the chloride ions. This ion exchangereaction, therefore, produces water as sodium chloride is adsorbed ontothe resins. The resins used in ion exchange do not absorb significantamounts of water.

[0013] The most efficient ion exchange occurs when strong acid andstrong base resins are employed. However, weak acid and weak base resinsalso can be used to deionize saline solutions. The efficiency of variouscombinations of acid and base exchange resins are as follows:

[0014] Strong acid—strong base (most efficient)

[0015] Weak acid—strong base

[0016] Strong acid—weak base

[0017] Weak acid—weak base (least efficient).

[0018] The weak acid/weak base resin combination requires that a “mixedbed” configuration be used to obtain deionization. The strongacid/strong base resin combination does not necessarily require a mixedbed configuration to deionize water. Deionization also can be achievedby sequentially passing the electrolyte-containing solution through astrong acid resin and strong base resin.

[0019] A “mixed bed” configuration of the prior art is a physicalmixture of an acid ion exchange resin and a base ion exchange resin inan ion exchange column, as disclosed in Battaerd U.S. Pat. No.3,716,481. Other patents directed to ion exchange resins having one ionexchange resin imbedded in a second ion exchange resin are Hatch U.S.Pat. No. 3,957,698, Wade et al. U.S. Pat. No. 4,139,499, Eppinger et al.U.S. Pat. No. 4,229,545, and Pilkington U.S. Pat. No. 4,378,439.Composite ion exchange resins also are disclosed in Hatch U.S. Pat. Nos.3,041,092 and 3,332,890, and Weiss U.S. Pat. No. 3,645,922.

[0020] The above patents are directed to nonswelling resins that can beused to remove ions from aqueous fluids, and thereby provide purifiedwater. Ion exchange resins used for water purification must not absorbsignificant amounts of water because resin swelling resulting fromabsorption can lead to bursting of the ion exchange containment column.

[0021] Ion exchange resins or fibers also have been disclosed for use inabsorbent personal care devices (e.g., diapers) to control the pH offluids that reach the skin, as set forth in Berg et al., U.S. Pat. No.4,685,909. The ion exchange resin is used in this application to reducediaper rash, but the ion exchange resin is not significantly waterabsorbent and, therefore, does not improve the absorption and retentionproperties of the diaper.

[0022] Ion exchange resins having a composite particle containing acidand base ion exchange particles embedded together in a matrix resin, orhaving acid and base ion exchange particles adjacent to one another in aparticle that is free of a matrix resin are disclosed in B. A. Bolto etal., J. Polymer Sci.:Symposium No. 55, John Wiley and Sons, Inc. (1976),pages 87-94. The Bolto et al. publication is directed to improving thereaction rates of ion exchange resins for water purification and doesnot utilize resins that absorb substantial amounts of water.

[0023] Other investigators have attempted to counteract the saltpoisoning effect and thereby improve the performance of SAPs withrespect to absorbing electrolyte-containing liquids, such as menses andurine. For example, Tanaka et al. U.S. Pat. No. 5,274,018 discloses anSAP composition comprising a swellable hydrophilic polymer, such aspolyacrylic acid, and an amount of an ionizable surfactant sufficient toform at least a monolayer of surfactant on the polymer. In anotherembodiment, a cationic gel, such as a gel containing quaternizedammonium groups and in the hydroxide (i.e., OH) form, is admixed with ananionic gel (i.e., a polyacrylic acid) to remove electrolytes from thesolution by ion exchange. Quaternized ammonium groups in the hydroxideform are very difficult and time-consuming to manufacture, therebylimiting the practical use of such cationic gels.

[0024] Wong U.S. Pat. No. 4,818,598 discloses the addition of a fibrousanion exchange material, such as DEAE (diethylaminoethyl) cellulose, toa hydrogel, such as a polyacrylate, to improve absorption properties.The ion exchange resin “pretreats” the saline solution (e.g., urine) asthe solution flows through an absorbent structure (e.g., a diaper). Thispretreatment removes a portion of the salt from the saline. Theconventional SAP present in the absorbent structure then absorbs thetreated saline more efficiently than untreated saline. The ion exchangeresin, per se, does not absorb the saline solution, but merely helpsovercome the “salt poisoning” effect.

[0025] WO 96/17681 discloses admixing discrete anionic SAP particles,such as polyacrylic acid, with discrete polysaccharide-based cationicSAP particles to overcome the salt poisoning effect. Similarly, WO96/15163 discloses combining a cationic SAP having at least 20% of thefunctional groups in a basic (i.e., OH) form with a cationic exchangeresin, i.e., a nonswelling ion exchange resin, having at least 50% ofthe functional groups in the acid form. WO 96/15180 discloses anabsorbent material comprising an anionic SAP, e.g., a polyacrylic acidand an anion exchange resin, i.e., a nonswelling ion exchange resin.

[0026] SAP particles in fiber form are known. For example, Allen U.S.Pat. No. 5,147,956 and Allen et al. U.S. Pat. Nos. 4,962,172; 4,861,539;and 4,280,079 disclose absorbent products and their method ofmanufacture. Farrar et al. U.S. Pat. No. 4,997,714 also disclosesabsorbent products in a fiber form, and their method of manufacture.Additional patents include Morgan U.S. Pat. No. 3,867,499, Funk U.S.Pat. No. 4,913,869, and Tai et al. U.S. Pat. No. 5,667,743. GB 2,269,602discloses a wet-laid nonwoven fabric comprising a blend of SAP fibersand a less absorbing fiber, like woodpulp. European Patent Application 0425 269 discloses a melt spun fiber containing a conventional syntheticmaterial and an SAP. WO 98/24832 discloses an absorbent compositioncontaining an acidic and basic material. The absorbent composition canbe in a fiber form. Further patents directed to fibers include WO96/JP651, WO 97/43480, and Hills U.S. Pat. No. 5,162,074.

[0027] Various references disclose combinations that attempt to overcomethe salt poisoning effect. However, the references do not teach SAPfibers having the improved fluid absorption and retention properties, orabsorption kinetics, demonstrated by the fibers of the presentinvention, which comprise at least one microdomain of an acidic resin incontact, or in close proximity, with at least one microdomain of a basicresin. These references also do not teach a mixture of resin particleswherein one component of the mixture is fibers of a multicomponent SAP.

[0028] The present invention, therefore, is directed to discrete SAPfibers that exhibit exceptional water absorption and retentionproperties, especially with respect to electrolyte-containing liquids,and thereby overcome the salt poisoning effect. In addition, thediscrete SAP fibers have an ability to absorb liquids quickly,demonstrate good fluid permeability and conductivity into and throughthe SAP fiber, and have a high gel strength such that the hydrogelformed from the SAP fibers does not deform or flow under an appliedstress or pressure, when used alone or in a mixture with otherwater-absorbing resins.

SUMMARY OF THE INVENTION

[0029] The present invention is directed to multicomponent SAPs, infiber form, comprising at least one acidic water-absorbing resin, suchas a polyacrylic acid, and at least one basic water-absorbing resin,such as a poly(vinylamine), a polyethyleneimine, or apoly(dialkylaminoalkyl acrylamide) or a poly(dialkylaminoalkylmethacrylamide), hereafter collectively referred to aspoly(dialkylaminoalkyl(meth)acrylamides).

[0030] More particularly, the present invention is directed tomulticomponent SAP fibers containing at least one discrete microdomainof at least one acidic water-absorbing resin in contact with, or inclose proximity to, at least one microdomain of at least one basicwater-absorbing resin. The acidic resin can be a strong or a weak acidicresin. Similarly, the basic resin can be a strong or a weak basic resin.

[0031] A preferred SAP contains one or more microdomains of at least oneweak acidic resin and one or more microdomains of at least one weakbasic resin. The properties demonstrated by such preferredmulticomponent SAP particles are unexpected because, in ion exchangeapplications, the combination of a weak acid and a weak base is theleast effective of any combination of a strong or weak acid ion exchangeresin with a strong or weak basic ion exchange resin.

[0032] The multicomponent SAP fibers can contain a plurality ofmicrodomains of the acidic water-absorbing resin and/or the basicwater-absorbing resin dispersed throughout the particle. Alternatively,the multicomponent SAP fibers can be in the form of a core and sheath,wherein the core is a microdomain of a first water-absorbing resin andthe sheath is a microdomain of a second water-absorbing resin. Themulticomponent SAP fibers also can be in the form of a fiber of anacidic water-absorbing resin and a fiber of a basic water-absorbingresin that are twisted together in the form of a braid or rope.

[0033] Accordingly, one aspect of the present invention is to provideSAP fibers that have a high absorption rate, have good permeability andgel strength, overcome the salt poisoning effect, and demonstrate animproved ability to absorb and retain electrolyte-containing liquids,such as saline, blood, urine, and menses. The present SAP fibers containdiscrete microdomains of acidic and basic resin, and during hydration,the fibers resist coalescence but remain fluid permeable.

[0034] Another aspect of the present invention is to provide an SAPhaving improved absorption and retention properties compared to aconventional SAP, such as sodium polyacrylate. The presentmulticomponent SAP fibers are produced by any method that positions amicrodomain of an acidic water-absorbing resin in contact with, or inclose proximity to, a microdomain of a basic water-absorbing resin toprovide a discrete particle. Such SAP particles demonstrate improvedabsorption and retention properties, and permeability through andbetween particles compared to SAP compositions comprising a simpleadmixture of acidic resin particles and basic resin particles.

[0035] In one embodiment, the SAP fibers are produced by coextruding anacidic water-absorbing hydrogel and a basic water-absorbing hydrogel toprovide multicomponent SAP fibers having a plurality of discretemicrodomains of an acidic resin and a basic resin dispersed throughoutthe particle. In another embodiment, the present multicomponent SAPfibers can be prepared by admixing dry particles of a basic resin with ahydrogel of an acidic resin, then extruding the resulting mixture toform multicomponent SAP fibers having microdomains of a basic resindispersed throughout a continuous phase of an acidic resin.Alternatively, dry acidic resin particles can be admixed with a basicresin hydrogel, followed by extruding the resulting mixture to formmulticomponent SAP fibers having microdomains of an acidic resindispersed in a continuous phase of a basic resin.

[0036] In addition, a multicomponent SAP fiber containing microdomainsof an acidic resin and a basic resin dispersed in a continuous phase ofa matrix resin can be prepared by adding dry particles of the acidicresin and dry particles of the basic resin to a hydrogel of the matrixhydrogel, then extruding.

[0037] In other embodiments, the acidic and basic water-absorbinghydrogels are coextruded, or spun, to form a fiber having a core-sheathconfiguration. Alternatively, the acidic and basic water-absorbinghydrogels are extruded, or spun, individually, then twisted together, inthe form of a braid, to provide a multicomponent SAP fiber.

[0038] In accordance with yet another important aspect of the presentinvention, the acidic and basic resins are lightly crosslinked, such aswith a suitable polyfunctional vinyl polymer. In preferred embodiments,the acidic resin, the basic resin, and/or the entire multicomponent SAPfiber are surface treated or annealed to further improve waterabsorption and retention properties, especially under a load.

[0039] Yet another important feature of the present invention is toprovide an SAP fiber containing at least one microdomain of a weakacidic water-absorbing resin in contact with at least one microdomain ofa weak basic water-absorbing resin.

[0040] An example of a weak acidic resin is polyacrylic acid having 0%to 25% neutralized carboxylic acid groups (i.e., DN=0 to DN=25).Examples of weak basic water-absorbing resins are a poly(vinylamine), apolyethylenimine, and a poly(dialkylaminoalkyl (meth)acrylamide)prepared from a monomer either having the general structure formula (I)

[0041] or the ester analog of (I) having the general structure formula(II)

[0042] wherein R₁ and R₂, independently, are selected from the groupconsisting of hydrogen and methyl, Y is a divalent straight chain orbranched organic radical having 1 to 8 carbon atoms, and R₃ and R₄,independently, are alkyl radicals having 1 to 4 carbon atoms. Examplesof a strong basic water-absorbing resin are poly(vinylguanidine) andpoly(allylguanidine).

[0043] Yet another aspect of the present invention is to provide animproved SAP material comprising a combination containing (a)multicomponent SAP fibers, and (b) particles of a second water-absorbingresin selected from the group consisting of an acidic water-absorbingresin, a basic water-absorbing resin, and a mixture thereof. Thecombination contains about 10% to about 90%, by weight, multicomponentSAP fibers and about 10% to about 90%, by weight, particles of thesecond water-absorbing resin.

[0044] Another important aspect of the present invention is to provide amethod of continuously producing core-sheath multicomponent SAP fibers.In one embodiment, a poly(vinylamine) core is prepared using a wetspinning method, which then is immediately directed to a solutioncontaining poly(acrylic acid) and a crosslinker. The freshly spunpoly(vinylamine) fiber, therefore, has a sheath of poly(acrylic acid)applied thereto.

[0045] Still another aspect of the present invention is to providediapers having a core comprising multicomponent SAP fibers or an SAPmaterial of the present invention. Other articles that can contain themulticomponent SAP fibers or an SAP material of the present inventioninclude catamenial devices, adult incontinence products, and devices forabsorbing saline and other ion-containing fluids.

[0046] These and other aspects and advantages of the present inventionwill become apparent from the following detailed description of thepreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIG. 1 is a cross-sectional view of a water-absorbing fibercontaining microdomains of a first resin dispersed in a continuous phaseof a second resin;

[0048]FIG. 2 is a cross-sectional view of a water-absorbing particlecontaining microdomains of a first resin and microdomains of a secondresin dispersed throughout the particle;

[0049]FIGS. 3A and 3B are cross-sectional views of a water-absorbingfiber having a core microdomain of a first resin surrounded by a sheathmicrodomain of a second resin;

[0050]FIGS. 4A and 4B are cross-sectional views of water-absorbingfibers having a microdomain of a first resin in contact with amicrodomain of a second resin;

[0051]FIGS. 5A and 5B are schematic diagrams of a water-absorbing fiberhaving individual fibers of a first and a second water-absorbing resintwisted together to form a rope;

[0052]FIG. 6 contains plots of absorbance (in grams of synthetic urineper gram of multicomponent SAP granules) vs. annealing temperature for aone-hour annealing step;

[0053]FIG. 7 contains a plot of absorbance (in grams of synthetic urineper gram of multicomponent SAP granules) vs. time for an annealing stepperformed at 125° C.;

[0054]FIG. 8 is a schematic illustration of a dry spinning apparatus;

[0055]FIG. 9 is a schematic illustration of a wet spinning apparatus;

[0056]FIG. 10 contains plots of AUL (0.28 psi) (g/g) vs. time for rateof absorption of twisted SAP fibers cured at 125° C. for 20 mins.; and

[0057]FIGS. 11 and 12 are scanning electron micrographs of themulticomponent SAP fibers of Example 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] The present invention is directed to multicomponent SAPparticles, in fiber form, containing at least one microdomain of anacidic water-absorbing resin in close proximity to, and preferably incontact with, at least one microdomain of a basic water-absorbing resin.Each fiber particle contains one or more microdomains of an acidic resinand one or more microdomains of a basic resin. The microdomains can bedistributed nonhomogeneously or homogeneously throughout each fiberparticle.

[0059] Each multicomponent SAP fiber of the present invention containsat least one acidic water-absorbing resin and at least one basicwater-absorbing resin. In one embodiment, the SAP fibers consistessentially of acidic resins and basic resins, and contain microdomainsof the acidic and/or basic resins. In another embodiment, microdomainsof the acidic and basic resins are dispersed in an absorbent matrixresin.

[0060] The multicomponent SAP particles of the present invention are inthe shape of a fiber. It is important that substantially each SAPparticle contain at least one microdomain of an acidic water-absorbingresin and at least one microdomain of a basic water-absorbing resin inclose proximity to one another. Improved water absorption and retention,and improved fluid permeability through and between SAP particles, areobserved as long as the acidic resin microdomain and the basic resinmicrodomain are in close proximity within the particle. In a preferredembodiment, the microdomains of acidic and basic resin are in contact.

[0061] In some embodiments, an idealized multicomponent SAP fiber of thepresent invention is analogous to a liquid emulsion wherein smalldroplets of a first liquid, i.e., the dispersed phase, are dispersed ina second liquid, i.e., the continuous phase. The first and secondliquids are immiscible, and the first liquid, therefore, ishomogeneously dispersed in the second liquid. The first liquid can bewater or oil based, and conversely, the second liquid is oil or waterbased, respectively.

[0062] Therefore, in one embodiment, the multicomponent SAP fibers ofthe present invention can be envisioned as one or more microdomains ofan acidic resin dispersed in a continuous phase of a basic resin, or asone or more microdomains of a basic resin dispersed in a continuous acidresin. These idealized multicomponent SAP fibers are illustrated in FIG.1 showing a cross section of an SAP fiber 10 having discretemicrodomains 14 of a dispersed resin in a continuous phase of a secondresin 12. If microdomains 14 comprise an acidic resin, then continuousphase 12 comprises a basic resin. Conversely, if microdomains 14comprise a basic resin, then continuous phase 12 is an acidic resin.

[0063] In another embodiment, the SAP fibers are envisioned asmicrodomains of an acidic resin and microdomains of a basic resindispersed throughout each particle, without a continuous phase. Thisembodiment is illustrated in FIG. 2, showing a cross section of anidealized multicomponent SAP fiber 20 having a plurality of microdomainsof an acidic resin 22 and a plurality of microdomains of a basic resin24 dispersed throughout fiber 20.

[0064] In yet another embodiment, microdomains of the acidic and basicresins are dispersed throughout a continuous phase comprising a matrixresin. This embodiment also is illustrated in FIG. 1 whereinmulticomponent SAP fiber 10 contains one or more microdomains 14, eachan acidic resin or a basic resin, dispersed in a continuous phase 12 ofa matrix resin.

[0065] It should be understood that the microdomains within each fibercan be of regular or irregular shape, and that the microdomains can bedispersed homogeneously or nonhomogeneously throughout each particle.Accordingly, another important embodiment of the SAP fiber isillustrated in FIG. 3A, showing an idealized multicomponent fiber 30having a core 32 of an acidic water-absorbing resin surrounded by asheath 34 of a basic water-absorbing resin. Conversely, core 32 cancomprise a basic resin, and sheath 34 can comprise an acidic resin.

[0066]FIG. 3B illustrates, in cross section, a similar embodiment havinga core and concentric sheaths that alternate between sheaths of acidicresin and basic resin. In one embodiment, core 42 and sheath 46 comprisean acidic water-absorbing resin, and shell 44 comprises a basicwater-absorbing resin. Other embodiments include: core 42 and sheath 46comprising a basic resin and sheath 44 comprising an acidic resin, orcore 42 comprising a matrix resin and sheaths 44 and 46 comprising anacidic resin and a basic resin in alternating shells. Otherconfigurations are apparent to persons skilled in the art, such asincreasing the number of shells around the core.

[0067]FIG. 4A illustrates another embodiment of the present SAP fibers,in cross section, wherein one microdomain 52 of an acidicwater-absorbing resin is in contact with one microdomain 54 of a basicwater-absorbing resin to provide a multicomponent SAP fiber 50. In thisembodiment, a surface of an acidic resin is in contact with a surface ofa microdomain of a basic resin. The embodiment illustrated in FIG. 4Aextends to SAP fibers having more than one microdomain of each of theacidic resin and the basic resin, as illustrated in FIG. 4B, wherein, incross section, multicomponent SAP fiber 70 contains alternating zones ofacidic water-absorbing resin 72 and basic water-absorbing resin 74.Fiber 70 also can contain one or more layers 72 or 74 comprising amatrix resin.

[0068] In another embodiment, the multicomponent SAP fiber comprisesindividual filaments of acidic resin and basic resin that are twistedtogether in the form of a rope. This embodiment is illustrated in FIGS.5A and B, which illustrate a “twisted rope” embodiment of the presentSAP fibers lengthwise and in cross section, respectively. In FIGS. 5Aand B, a multicomponent SAP particle 80 comprises a filament 82 ofacidic water-absorbing resin and a filament 84 of basic water-absorbingresin. Filaments 82 and 84 are in contact along zone of contact 86,thereby placing the acidic and basic resins in contact.

[0069] The “twisted rope” SAP fibers of FIGS. 5A and B also can be anembodiment wherein acidic resin filament 82 contains microdomains of abasic water-absorbing resin, i.e., is a multicomponent SAP fiber itself,and/or basic resin filament 84 contains microdomains of an acidicwater-absorbing resin, i.e., also is a multicomponent SAP fiber itself.Filaments 82 and 84 then are intertwined to form multicomponent SAPfiber 80.

[0070] The embodiment of FIGS. 5A and B also can be a filament 82 and/ora filament 84 comprising a matrix resin having microdomains of acidicresin and/or basic resin. In this embodiment, filament 82 containsmicrodomains of an acidic resin, or microdomains of an acidic and abasic resin, and filament 84 contains microdomains of a basic resin, ormicrodomains of an acidic resin and a basic resin.

[0071] The multicomponent SAP fibers of the present invention comprisean acidic resin and a basic resin in a weight ratio of about 95:5 toabout 5:95, and preferably about 15:85 to about 85:15. To achieve thefull advantage of the present invention, the weight ratio of acidicresin to basic resin in a multicomponent SAP fiber is about 30:70 toabout 70:30. The acidic and basic resins can be distributedhomogeneously or nonhomogeneously throughout the SAP fiber.

[0072] The present multicomponent SAP fibers contain at least about 50%,and preferably at least about 70%, by weight of acidic resin plus basicresin. To achieve the full advantage of the present invention, amulticomponent SAP fiber contains about 80% to 100% by weight of theacidic resin plus basic resin. Components of the present SAP fibers,other than the acidic and basic resin, typically, are matrix resins orother minor optional ingredients.

[0073] The multicomponent SAP fibers of the present invention can be ofany cross-sectional geometry. The multicomponent SAP fibers can beprepared using an extrusion step. In such a case, the shape of the SAPfiber is determined by the shape of the extrusion die. The shape of themulticomponent SAP fibers also can be determined by other methods ofpreparing the particles, such wet or dry spinning, which are thepreferred methods of preparation.

[0074] In accordance with the present invention, a microdomain isdefined as a volume of an acidic resin or a basic resin that is presentin a multicomponent SAP fiber. Because each multicomponent SAP particlecontains at least one microdomain of an acidic resin, and at least onemicrodomain of a basic resin, a microdomain has a volume that is lessthan the volume of the multicomponent SAP fiber. A microdomain,therefore, can be as large as about 90% of the volume of multicomponentSAP fibers.

[0075] The multicomponent SAP fibers of the present invention areelongated, acicular SAP particles. The fiber can be in the shape of acylinder, for example, having a minor dimension (i.e., diameter) and amajor dimension (i.e., length). The fiber also can be in the form of along filament that can be woven. Such filament-like fibers have a weightof below about 80 decitex, and preferably below about 70 decitex, perfilament, for example, about 2 to about 60 decitex per filament. Tex isthe weight in grams per one kilometer of fiber. One tex equals 10decitex. For comparison, poly(acrylic acid) is about 0.78 decitex (0.078tex), and poly(vinylamine) is about 6.1 decitex (0.61 tex).

[0076] Cylindrical multicomponent SAP fibers have a minor dimension(i.e., diameter of the fiber) less than about 1 mm, usually less thanabout 500 μm, and preferably less than 250 μm, down to about 10 μm. Thecylindrical SAP fibers can have a relatively short major dimension, forexample, about 1 mm, e.g., in a fibril, lamella, or flake-shapedarticle, but generally the fiber has a length of about 3 to about 100mm. The filament-like fibers have a ratio of major dimension to minordimension of at least 500 to 1, and preferably at least 1000 to 1, forexample, up to and greater than 10,000 to 1.

[0077] Typically, a microdomain within a fiber or a filament of a fiberhas a diameter of about 750 μm or less, and preferably about 100 μm orless. To achieve the full advantage of the present invention, amicrodomain has a diameter of about 20 μm or less. The multicomponentSAP fibers also contain microdomains that have submicron diameters,e.g., microdomain diameters of less than 1 μm to about 0.01 μm. In otherembodiments, the microdomain can be the entire filament of a twistedrope SAP fiber. Microdomains also can be the core and the sheath in theembodiments illustrated in FIGS. 3A and B.

[0078] Each multicomponent SAP fiber contains one or more microdomainsof an acidic water-absorbing resin and one or more microdomains of abasic water-absorbing resin, either in contact or in close proximity toone another. As illustrated hereafter, the microdomain structure of thepresent SAP fibers provides improved fluid absorption (both in amount offluid absorbed and retained, and rate of absorption) compared to an SAPcomprising a simple mixture of discrete acidic SAP resin fibers anddiscrete basic SAP resin fibers. In accordance with another importantfeature of the present invention, the present multicomponent SAP fibersalso demonstrate improved permeability, both through an individual fiberand between fibers. The present SAP fibers, therefore, have an improvedability to rapidly absorb a fluid, even in “gush” situations, forexample, when used in diapers to absorb urine.

[0079] The features of good permeability, absorption and retentionproperties, especially of electrolyte-containing liquids, demonstratedby the present multicomponent SAP fibers, is important with respect topractical uses of an SAP. These improved properties are attributed, inpart, to the fact that electrolyte removal from the liquid isfacilitated by contacting a single particle (which, in effect, performsan essentially simultaneous deionization of the liquid), as opposed tothe liquid having to contact individual acidic and basic particles(which, in effect, performs a sequential two-step deionization).

[0080] If a blend of acidic resin fibers and basic resin fibers is used,the fibers typically have a small particle size. A small particle sizeis required to obtain desirable desalination kinetics, because theelectrolyte is removed in a stepwise manner, with the acidic resinremoving the cation and the basic resin removing the anion. Theelectrolyte-containing fluid, therefore, must contact two particles fordesalination, and this process is facilitated by small particle sizedSAPs. Small particles, however, have the effect of reducing flow of thefluid through and between SAP particles, i.e., permeability is reducedand a longer time is required to absorb the fluid.

[0081] In addition, in practical use, such as in diapers, SAPs are usedin conjunction with a cellulosic pulp. If a blend of acidic resinparticles and basic resin particles is used as the SAP, the cellulosicpulp can cause a separation between the acidic resin particles and basicresin particles, which adversely affects desalination. The presentmultidomain SAP fibers overcome this problem because the acidic resinand basic resin are present in a single particle. The introduction ofcellulosic pulp, therefore, cannot separate the acidic and basic resinand cannot adversely affect desalination by the SAP.

[0082] A single multicomponent SAP particle, like a present fiber,simultaneously desalinates an electrolyte-containing liquid.Desalination is essentially independent of particle size. Accordingly,the present multicomponent SAP fibers can be of a larger size. Thesefeatures allow for improved liquid permeability through and between theSAP particles, and results in a more rapid absorption of theelectrolyte-containing liquid.

[0083] The following schematic reactions illustrate the reactions whichoccur to deionize, e.g., desalinate, an aqueous saline solution, andthat are performed essentially simultaneously in a single microcompositeSAP particle, but are performed stepwise in a simple mixture of acidicand basic resins:

R—CO₂H+NaCl→R—CO₂ ⁻Na⁺+HCl

[0084] (acidic resin)

R—NH₂+HCl→R—NH₃ ⁺Cl⁻

[0085] (basic resin).

[0086] The present multicomponent SAP fibers can be in a form wherein amicrodomain of an acidic water-absorbing resin is in contact with amicrodomain of a basic water-absorbing resin. In another embodiment, theSAP fibers can be in a form wherein at least one microdomain of anacidic water-absorbing resin is dispersed in a continuous phase of abasic water-absorbing resin. Alternatively, the multicomponent SAPfibers can be in a form wherein at least one microdomain of a basicresin is dispersed in a continuous phase of an acidic resin. In anotherembodiment, at least one microdomain of one or more acidic resin and atleast one microdomain of one or more basic resin comprise the entire SAPfiber, and neither type of resin is considered the dispersed or thecontinuous phase. In yet another embodiment, at least one microdomain ofan acidic resin and at least one microdomain of a basic resin aredispersed in a matrix resin.

[0087] An acidic water-absorbing resin present in a multicomponent SAPfiber can be either a strong or a weak acidic water-absorbing resin. Theacidic water-absorbing resin can be a single resin, or a mixture ofresins. The acidic resin can be a homopolymer or a copolymer. Theidentity of the acidic water-absorbing resin is not limited as long asthe resin is capable of swelling and absorbing at least ten times itsweight in water, when in a neutralized form. The acidic resin is presentin its acidic form, i.e., about 75% to 100% of the acidic moieties arepresent in the free acid form. As illustrated hereafter, although thefree acid form of a acidic water-absorbing resin is generally a poorwater absorbent, the combination of an acidic resin and a basic resin ina present multicomponent SAP fiber provides excellent water absorptionand retention properties.

[0088] The acidic water-absorbing resin typically is a lightlycrosslinked acrylic-type resin, such as lightly crosslinked polyacrylicacid. The lightly crosslinked acidic resin typically is prepared bypolymerizing an acidic monomer containing an acyl moiety, e.g., acrylicacid, or a moiety capable of providing an acid group, i.e.,acrylonitrile, in the presence of a crosslinker, i.e., a polyfunctionalorganic compound. The acidic resin can contain other copolymerizableunits, i.e., other monoethylenically unsaturated comonomers, well knownin the art, as long as the polymer is substantially, i.e., at least 10%,and preferably at least 25%, acidic monomer units. To achieve the fulladvantage of the present invention, the acidic resin contains at least50%, and more preferably, at least 75%, and up to 100%, acidic monomerunits. The other copolymerizable units can, for example, help improvethe hydrophilicity and crosslinking of the polymer.

[0089] Ethylenically unsaturated carboxylic acid and carboxylic acidanhydride monomers useful in the acidic water-absorbing resin includeacrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid,α-cyanoacrylic acid, β-methylacrylic acid (crotonic acid),α-phenylacrylic acid, β-acryloxypropionic acid, sorbic acid,α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid,β-stearylacrylic acid, itaconic acid, citraconic acid, mesaconic acid,glutaconic acid, aconitic acid, maleic acid, fumaric acid,tricarboxyethylene, and maleic anhydride.

[0090] Ethylenically unsaturated sulfonic acid monomers includealiphatic or aromatic vinyl sulfonic acids, such as vinylsulfonic acid,allyl sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid,acrylic and methacrylic sulfonic acids, such as sulfoethyl acrylate,sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate,2-hydroxy-3-methacryloxypropyl sulfonic acid, and2-acrylamide-2-methylpropane sulfonic acid.

[0091] As set forth above, polymerization of acidic monomers, andcopolymerizable monomers, if present, most commonly is performed by freeradical processes in the presence of a polyfunctional organic compound.The acidic resins are crosslinked to a sufficient extent such that thepolymer is water insoluble. Crosslinking renders the acidic resinssubstantially water insoluble, and, in part, serves to determine theabsorption capacity of the resins. For use in absorption applications,an acidic resin is lightly crosslinked, i.e., has a crosslinking densityof less than about 20%, preferably less than about 10%, and mostpreferably about 0.01% to about 7%.

[0092] A crosslinking agent most preferably is used in an amount of lessthan about 7 wt %, and typically about 0.1 wt % to about 5 wt %, basedon the total weight of monomers. Examples of crosslinking polyvinylmonomers include, but are not limited to, polyacrylic (orpolymethacrylic) acid esters represented by the following formula (III);and bisacrylamides, represented by the following formula (IV).

[0093] wherein x is ethylene, propylene, trimethylene, cyclohexyl,hexamethylene, 2-hydroxypropylene, —(CH₂CH₂O)_(n)CH₂CH₂—, or

[0094] n and m are each an integer 5 to 40, and k is 1 or 2;

[0095] wherein 1 is 2 or 3.

[0096] The compounds of formula (III) are prepared by reacting polyols,such as ethylene glycol, propylene glycol, trimethylolpropane,1,6-hexanediol, glycerin, pentaerythritol, polyethylene glycol, orpolypropylene glycol, with acrylic acid or methacrylic acid. Thecompounds of formula (IV) are obtained by reacting polyalkylenepolyamines, such as diethylenetriamine and triethylenetetramine, withacrylic acid.

[0097] Specific crosslinking monomers include, but are not limited to,1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,3-butyleneglycol diacrylate, 1,3-butylene glycol dimethacrylate, diethylene glycoldiacrylate, diethylene glycol dimethacrylate, ethoxylated bisphenol Adiacrylate, ethoxylated bisphenol A dimethacrylate, ethylene glycoldimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanedioldimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycoldiacrylate, polyethylene glycol dimethacrylate, triethylene glycoldiacrylate, triethylene glycol dimethacrylate, tripropylene glycoldiacrylate, tetraethylene glycol diacrylate, tetraethylene glycoldimethacrylate, dipentaerythritol pentaacrylate, pentaerythritoltetraacrylate, pentaerythritol triacrylate, trimethylolpropanetriacrylate, trimethylolpropane trimethacrylate,tris(2-hydroxyethyl)isocyanurate triacrylate,tris(2-hydroxyethyl)isocyanurate trimethacrylate, divinyl esters of apolycarboxylic acid, diallyl esters of a polycarboxylic acid, triallylterephthalate, diallyl maleate, diallyl fumarate,hexamethylenebismaleimide, trivinyl trimellitate, divinyl adipate,diallyl succinate, a divinyl ether of ethylene glycol, cyclopentadienediacrylate, tetraallyl ammonium halides, or mixtures thereof. Compoundssuch as divinylbenzene and divinyl ether also can be used to crosslinkthe poly(dialkylaminoalkyl acrylamides). Especially preferredcrosslinking agents are N,N′-methylenebisacrylamide,N,N′-methylenebismethacrylamide, ethylene glycol dimethacrylate, andtrimethylolpropane triacrylate.

[0098] The acidic resin, either strongly acidic or weakly acidic, can beany resin that acts as an SAP in its neutralized form. The acidic resinstypically contain a plurality of carboxylic acid, sulfonic acid,phosphonic acid, phosphoric acid, and/or sulfuric acid moieties.Examples of acidic resins include, but are not limited to, polyacrylicacid, hydrolyzed starch-acrylonitrile graft copolymers, starch-acrylicacid graft copolymers, saponified vinyl acetate-acrylic estercopolymers, hydrolyzed acrylonitrile copolymers, hydrolyzed acrylamidecopolymers, ethylene-maleic anhydride copolymers, isobutylene-maleicanhydride copolymers, poly(vinylsulfonic acid), poly(vinylphosphonicacid), poly(vinylphosphoric acid), poly(vinylsulfuric acid), sulfonatedpolystyrene, poly(aspartic acid), poly(lactic acid), and mixturesthereof. The preferred acidic resins are the polyacrylic acids.

[0099] The multicomponent SAP fibers can contain individual microdomainsthat: (a) contain a single acidic resin or (b) contain more than one,i.e., a mixture, of acidic resins. The multicomponent SAP fibers alsocan contain microdomains wherein, for the acidic component, a portion ofthe acidic microdomains comprise a first acidic resin or acidic resinmixture, and the remaining portion comprises a second acidic resin oracidic resin mixture.

[0100] Analogous to the acidic resin, the basic water-absorbing resin inthe present SAP fibers can be a strong or weak basic water-absorbingresin. The basic water-absorbing resin can be a single resin or amixture of resins. The basic resin can be a homopolymer or a copolymer.The identity of the basic resin is not limited as long as the basicresin is capable of swelling and absorbing at least 10 times its weightin water, when in a charged form. The weak basic resin typically ispresent in its free base, or neutral, form, i.e., about 75% to about100% of the basic moieties, e.g., amino groups, are present in aneutral, uncharged form. The strong basic resins typically are presentin the hydroxide (OH) or bicarbonate (HCO₃) form.

[0101] The basic water-absorbing resin typically is a lightlycrosslinked acrylic type resin, such as a poly(vinylamine) or apoly(dialkylaminoalkyl (meth)acrylamide). The basic resin also can be apolymer such as a lightly crosslinked polyethylenimine, apoly(allylamine), a poly(allylguanidine), a poly(dimethyldiallylammoniumhydroxide), a quaternized polystyrene derivative, such as

[0102] a guanidine-modified polystyrene, such as

[0103] a quaternized poly((meth)acrylamide) or ester analog, such as

[0104] wherein Me is methyl, R₂ is hydrogen or methyl, n is a number 1to 8, and q is a number from 10 to about 100,000, or apoly(vinylguanidine), i.e., poly(VG), a strong basic water-absorbingresin having the general structural formula (V)

[0105] wherein q is a number from 10 to about 100,000, and R₅ and R₆,independently, are selected from the group consisting of hydrogen, C₁-C₄alkyl, C₃-C₆ cycloalkyl, benzyl, phenyl, alkyl-substituted phenyl,naphthyl, and similar aliphatic and aromatic groups. The lightlycrosslinked basic water-absorbing resin can contain othercopolymerizable units and is cross-linked using a polyfunctional organiccompound, as set forth above with respect to the acidic water-absorbingresin.

[0106] A basic water-absorbing resin used in the present SAP fiberstypically contains an amino or a guanidino group. Accordingly, awater-soluble basic resin also can be crosslinked in solution bysuspending or dissolving an uncrosslinked basic resin in an aqueous oralcoholic medium, then adding a di- or polyfunctional compound capableof crosslinking the basic resin by reaction with the amino groups of thebasic resin. Such crosslinking agents include, for example,multifunctional aldehydes (e.g., glutaraldehyde), multifunctionalacrylates (e.g., butanediol diacrylate, TMPTA), halohydrins (e.g.,epichlorohydrin), dihalides (e.g., dibromopropane), disulfonate esters(e.g., ZA(O₂)O—(CH₂)_(n)—OS(O)₂Z, wherein n is 1 to 10, and Z is methylor tosyl), multifunctional epoxies (e.g., ethylene glycol diglycidylether), multifunctional esters (e.g., dimethyl adipate), multifunctionalacid halides (e.g., oxalyl chloride), multifunctional carboxylic acids(e.g., succinic acid), carboxylic acid anhydrides (e.g., succinicanhydride), organic titanates (e.g., TYZOR AA from DuPont), melamineresins (e.g., CYMEL 301, CYMEL 303, CYMEL 370, and CYMEL 373 from CytecIndustries, Wayne, N.J.), hydroxymethyl ureas (e.g.,N,N′-dihydroxymethyl-4,5-dihydroxyethyleneurea), and multifunctionalisocyanates (e.g., toluene diisocyanate or methylene diisocyanate).Crosslinking agents also are disclosed in Pinschmidt, Jr. et al. U.S.Pat. No. 5,085,787, incorporated herein by reference, and in EP 450 923.

[0107] Conventionally, the crosslinking agent is water or alcoholsoluble, and possesses sufficient reactivity with the basic resin suchthat crosslinking occurs in a controlled fashion, preferably at atemperature of about 25° C. to about 150° C. Preferred crosslinkingagents are ethylene glycol diglycidyl ether (EGDGE), a water-solublediglycidyl ether, and a dibromoalkane, an alcohol-soluble compound.

[0108] The basic resin, either strongly or weakly basic, therefore, canbe any resin that acts as an SAP in its charged form. The basic resintypically contains amino or guanidino moieties. Examples of basic resinsinclude a poly(vinylamine), a polyethylenimine, a poly(vinylguanidine),a poly(allylamine), a poly(allylguanidine), or a poly(dialkylaminoalkyl(meth)acrylamide) prepared by polymerizing and lightly crosslinking amonomer having the structure

[0109] wherein R₁ and R₂, independently, are selected from the groupconsisting of hydrogen and methyl, Y is a divalent straight chain orbranched organic radical having 1 to 8 carbon atoms, and R₃ and R₄,independently, are alkyl radicals having 1 to 4 carbon atoms. Preferredbasic resins include a poly(vinylamine), polyethylenimine,poly(vinylguanadine), poly(dimethylaminoethyl acrylamide) (poly(DAEA)),and poly(dimethylaminopropyl methacrylamide) (poly(DMAPMA)). Analogousto microdomains of an acidic resin, the present multicomponent SAPs cancontain microdomains of a single basic resin, microdomains containing amixture of basic resins, or microdomains of different basic resins.

[0110] The present multicomponent SAP fibers can be prepared by variousmethods, and the method of preparing a multicomponent SAP fiber is notlimited by the following embodiments. Any method that provides a fiberhaving at least one microdomain of an acidic resin in contact with or inclose proximity to at least one microdomain of a basic resin issuitable.

[0111] In one method, dry particles of a basic resin, optionally surfacecrosslinked and/or annealed, are admixed into a rubbery gel of an acidicresin. The resulting mixture is extruded, then dried, and optionallysurface crosslinked and/or annealed, to provide multicomponent SAPfibers having microdomains of a basic resin dispersed in a continuousphase of an acidic resin. Alternatively, particles of an acidic resin,optionally surface crosslinked and/or annealed, can be admixed into arubbery gel of a basic resin, and the resulting mixture is extruded anddried, and optionally surface crosslinked and/or annealed, to providemulticomponent SAP fibers having microdomains of an acidic resindispersed in a continuous phase of a basic resin.

[0112] In another method, dry particles of an acidic resin can beadmixed with dry particles of a basic resin, and the resulting mixtureis formed into a hydrogel, then extruded, to form multicomponent SAPfibers.

[0113] In yet another method, a rubbery gel of an acidic resin and arubbery gel of a basic resin, each optionally surface crosslinked and/orannealed, are coextruded, and the coextruded product is dried, andoptionally surface crosslinked and/or annealed, to form multicomponentSAP fibers containing microdomains of the acidic resin and the basicresin, as illustrated in FIGS. 3 and 4.

[0114] Another method utilizes spinning technology, wherein a firstpolymer, e.g., poly(vinylamine), is spun in the form of a filament, thenthe freshly spun filament is coated with a second polymer, e.g.,poly(acrylic acid), to form (after drying) a core-sheath multicomponentSAP fiber.

[0115] In yet another method, a filament of an acidic resin is preparedby standard spinning techniques, and a filament of a basic resin isprepared by standard spinning techniques. The two filaments then aretwisted together, before and/or after optional surface crosslinking andannealing, and then dried and formed into multicomponent SAP fibers, asillustrated in FIG. 5.

[0116] The method of preparing the present multicomponent SAP fibers,therefore, typically utilizes, but does not require, a spinning or anextrusion step. Other methods of preparation wherein the multicomponentSAP fiber contains at least one microdomain of an acidic resin and atleast one microdomain of a basic resin in contact or in close proximitywith each other also can be used.

[0117] In embodiments wherein an acidic resin and a basic resin arepresent as microdomains within a matrix of a matrix resin, particles ofan acidic resin and a basic resin are admixed with a rubbery gel of amatrix resin, and the resulting mixture is extruded, then dried, to formmulticomponent SAP fibers having microdomains of an acidic resin and abasic resin dispersed in a continuous phase of a matrix resin.Alternatively, rubbery gels of an acidic resin, basic resin, and matrixresin can be coextruded to provide a multicomponent SAP fiberscontaining microdomains of an acidic resin, a basic resin, and a matrixresin. In this embodiment, the acidic resin, basic resin, and resultingmulticomponent SAP fibers, each can be optionally surface crosslinkedand/or annealed. Similarly, the matrix resin, acidic resin, and basicresin can be spun to form a core-sheath or twisted SAP fiber embodimentof the multicomponent SAP fibers.

[0118] The matrix resin is any resin that allows fluid transport suchthat a liquid medium can contact the acidic and basic resin. The matrixresin typically is a hydrophilic resin capable of absorbing water.Nonlimiting examples of matrix resins include poly(vinyl alcohol),poly(N-vinylformamide), polyethylene oxide, poly(meth)acrylamide,poly(hydroxyethyl acrylate), hydroxyethylcellulose, methylcellulose, andmixtures thereof. The matrix resin also can be a conventionalwater-absorbing resin, for example, a polyacrylic acid neutralizedgreater than 25 mole %, and typically greater than 50 mole %.

[0119] In preferred embodiments, the acidic resin, the basic resin,and/or the multicomponent SAP particles are surface treated and/orannealed. Surface treatment and/or annealing results in surfacecrosslinking of the particle. In especially preferred embodiments, theacidic and/or basic resins comprising the multicomponent SAP fibers aresurface treated and/or annealed, and the entire multicomponent SAP fiberis surface treated and/or annealed. It has been found that surfacetreating and/or annealing of an acidic resin, a basic resin, and/or amulticomponent SAP fiber of the present invention enhances the abilityof the resin or multicomponent SAP fiber to absorb and retain aqueousmedia under a load.

[0120] Surface crosslinking is achieved by contacting an acidic resin, abasic resin, and/or a multicomponent SAP fiber with a solution of asurface crosslinking agent to wet predominantly only the outer surfacesof the resin or SAP particle. Surface crosslinking and drying of theresin or multicomponent SAP particle then is performed, preferably byheating at least the wetted surfaces of the resin or multicomponent SAPfibers.

[0121] Typically, the resins and/or SAP fibers are surface treated witha solution of a surface cross-linking agent. The solution contains about0.01% to about 4%, by weight, surface crosslinking agent, and preferablyabout 0.4% to about 2%, by weight, surface crosslinking agent in asuitable solvent, for example, water or an alcohol. The solution can beapplied as a fine spray onto the surface of freely tumbling resinparticles or multicomponent SAP particles at a ratio of about 1:0.01 toabout 1:0.5 parts by weight resin or SAP particles to solution ofsurface crosslinking agent. The surface crosslinker is present in anamount of 0% to about 5%, by weight of the resin or SAP fiber, andpreferably 0% to about 0.5% by weight. To achieve the full advantage ofthe present invention, the surface crosslinker is present in an amountof about 0.001% to about 0.1% by weight.

[0122] The crosslinking reaction and drying of the surface-treated resinor multicomponent SAP fibers are achieved by heating the surface-treatedpolymer at a suitable temperature, e.g., about 25° C. to about 150° C.,and preferably about 105° C. to about 120° C. However, any other methodof reacting the crosslinking agent to achieve surface crosslinking ofthe resin or multicomponent SAP fibers, and any other method of dryingthe resin or multicomponent SAP fibers, such as microwave energy, or thesuch as, can be used.

[0123] With respect to the basic resin, or multicomponent SAP fibershaving a basic resin present on the exterior of the fibers, suitablesurface crosslinking agents include di- or polyfunctional moleculescapable of reacting with amino groups and crosslinking a basic resin.Preferably, the surface crosslinking agent is alcohol or water solubleand possesses sufficient reactivity with a basic resin such thatcrosslinking occurs in a controlled fashion at a temperature of about25° C. to about 150° C.

[0124] Nonlimiting examples of suitable surface crosslinking agents forbasic resins include:

[0125] (a) dihalides and disulfonate esters, for example, compounds ofthe formula

Y—(CH₂)_(p)—Y,

[0126] wherein p is a number from 2 to 12, and Y, independently, is halo(preferably bromo), tosylate, mesylate, or other alkyl or aryl sulfonateesters;

[0127] (b) multifunctional aziridines;

[0128] (c) multifunctional aldehydes, for example, glutaraldehyde,trioxane, paraformaldehyde, terephthaldehyde, malonaldehyde, andglyoxal, and acetals and bisulfites thereof;

[0129] (d) halohydrins, such as epichlorohydrin;

[0130] (e) multifunctional epoxy compounds, for example, ethylene glycoldiglycidyl ether, bisphenol A diglycidyl ether, and bisphenol Fdiglycidyl ether,

[0131] (f) multifunctional carboxylic acids and esters, acid chlorides,and anhydrides derived therefrom, for example, di- and polycarboxylicacids containing 2 to 12 carbon atoms, and the methyl and ethyl esters,acid chlorides, and anhydrides derived therefrom, such as oxalic acid,adipic acid, succinic acid, dodecanoic acid, malonic acid, and glutaricacid, and esters, anhydrides, and acid chlorides derived therefrom;

[0132] (g) organic titanates, such as TYZOR AA, available from E. I.DuPont de Nemours, Wilmington, Del.;

[0133] (h) melamine resins, such as the CYMEL resins available fromCytec Industries, Wayne, N.J.;

[0134] (i) hydroxymethyl ureas, such asN,N′-dihydroxymethyl-4,5-dihydroxyethylene urea;

[0135] (j) multifunctional isocyanates, such as toluene diisocyanate,isophorone diisocyanate, methylene diisocyanate, xylene diisocyanate,and hexamethylene diisocyanate; and

[0136] (k) other crosslinking agents for basic water-absorbing resinsknown to persons skilled in the art.

[0137] A preferred surface crosslinking agent is a dihaloalkane,ethylene glycol diglycidyl ether (EGDGE), or a mixture thereof, whichcrosslink a basic resin at a temperature of about 25° C. to about 150°C. Especially preferred surface crosslinking agents are dibromoalkanescontaining 3 to 10 carbon atoms and EGDGE.

[0138] With respect to the acidic water-absorbing resins, ormulticomponent SAP particles having an acidic resin on the exterior ofthe fibers, suitable surface crosslinking agents are capable of reactingwith acid moieties and crosslinking the acidic resin. Preferably, thesurface crosslinking agent is alcohol soluble or water soluble, andpossesses sufficient reactivity with an acidic resin such thatcrosslinking occurs in a controlled fashion, preferably at a temperatureof about 25° C. to about 150° C.

[0139] Nonlimiting examples of suitable surface crosslinking agents foracidic resins include:

[0140] (a) polyhydroxy compounds, such as glycols and glycerol;

[0141] (b) metal salts;

[0142] (c) quaternary ammonium compounds;

[0143] (d) a multifunctional epoxy compound;

[0144] (e) an alkylene carbonate, such as ethylene carbonate orpropylene carbonate;

[0145] (f) a polyaziridine, such as 2,2-bishydroxymethyl butanoltris[3-(1-aziridine propionate]);

[0146] (g) a haloepoxy, such as epichlorhydrin;

[0147] (h) a polyamine, such as ethylenediamine;

[0148] (i) a polyisocyanate, such as 2,4-toluene diisocyanate; and

[0149] (j) other crosslinking agents for acidic water-absorbing resinsknown to persons skilled in the art.

[0150] In addition to, or in lieu of, surface treating, the acidicresin, the basic resin, the matrix resin, the entire SAP fiber, or anycombination thereof can be annealed to improve water absorption andretention properties under a load. It has been found that heating aresin for a sufficient time at a sufficient temperature above the Tg(glass transition temperature) of the resin or microdomains improves theabsorption properties of the resin. FIGS. 6 and 7 contain graphs showingthe effect of annealing time and temperature on the absorptionproperties of multicomponent SAP granules comprising 55% by weightpoly(vinylamine) and 45% by weight poly(acrylic acid). Typically, amulticomponent SAP fiber of the present invention is subjected to asufficient temperature for a sufficient time to heat and anneal theexternal and the internal portions of the fiber.

[0151] The graphs in FIGS. 6 and 7 show that heating a multicomponentSAP granule for about 20 to about 120 minutes at a temperature of about60° C. to about 150° C. improves absorption properties. The absorptionproperties, i.e., AUL and AUNL, graphed in FIGS. 6 and 7 are discussedin detail hereafter. Preferably, annealing is performed for about 30 toabout 100 minutes at about 80° C. to about 140° C. To achieve the fulladvantage of annealing, the SAP fibers are annealed for about 40 toabout 90 minutes at about 100° C. to about 140° C.

[0152] In accordance with an important feature of the present invention,a strong acidic resin can be used with either a strong basic resin or aweak basic resin, or a mixture thereof. A weak acidic resin can be usedwith a strong basic resin or a weak basic resin, or a mixture thereof.Preferably, the acidic resin is a weak acidic resin and the basic resinis a weak basic resin. This result is unexpected in view of the ionexchange art wherein a combination of a weak acidic resin and a weakbasic resin does not perform as well as other combinations, e.g., astrong acidic resin and a strong basic resin. In more preferredembodiments, the weak acidic resin, the weak basic resin, and/or themulticomponent SAP fibers are surface crosslinked and/or annealed.

[0153] As previously discussed, sodium poly(acrylate) conventionally isconsidered the best SAP, and, therefore, is the most widely used SAP incommercial applications. Sodium poly(acrylate) has polyelectrolyticproperties that are responsible for its superior performance inabsorbent applications. These properties include a high charge density,and charge relatively close to the polymer backbone.

[0154] However, an acidic resin in the free acid form, or a basic resinin the free base form, typically do not function as a commerciallyuseful SAP because there is no ionic charge on either type of polymer. Apoly(acrylic acid) resin, or a poly(vinylamine) resin, are neutralpolymers, and, accordingly, do not possess the polyelectrolyticproperties necessary to provide SAPs useful commercially in diapers,catamenial devices, and similar absorbent articles. The driving forcefor water absorption and retention, therefore, is lacking. This isillustrated in Tables 3 and 4 showing the relatively poor absorption andretention properties for a neutral poly(DAEA) in absorbing syntheticurine. However, when converted to a salt, an acidic resin, such as apolyacrylic acid, or a basic resin, such as a poly(dialkylaminoalkyl(meth)acrylamide), then behave such as a commercially useful SAP.

[0155] It has been found that basic resins, in their free base form, areuseful components in super-absorbent materials further containing anacidic water-absorbing resin. For example, a superabsorbent materialcomprising an admixture of a poly(dialkylaminoalkyl (meth)acrylamide)and an acidic water-absorbing resin, such as polyacrylic acid,demonstrates good water absorption and retention properties. Such an SAPmaterial comprises two uncharged, slightly crosslinked polymers, each ofwhich is capable of swelling and absorbing aqueous media. When contactedwith water or an aqueous electrolyte-containing medium, the twouncharged polymers neutralize each other to form a superabsorbentmaterial. This also reduces the electrolyte content of the mediumabsorbed by polymer, further enhancing the polyelectrolyte effect.Neither polymer in its uncharged form behaves as an SAP by itself whencontacted with water. However, superabsorbent materials, which contain asimple mixture of two resins, one acidic and one basic, are capable ofacting as an absorbent material because the two resins are converted totheir polyelectrolyte form. These superabsorbent materials havedemonstrated good water absorption and retention properties.

[0156] In the present multicomponent SAP fibers, the weak basic resin ispresent in its free base, e.g., amine, form, and the acidic resin ispresent in its free acid form. It is envisioned that a low percentage,i.e., about 25% or less, of the amine and/or acid functionalities can bein their charged form. The low percentage of charged functionalitiesdoes not adversely affect performance of the SAP fibers, and can assistin the initial absorption of a liquid. A strong basic resin is presentin the hydroxide or bicarbonate, i.e., charged, form.

[0157] The present multicomponent SAP fibers are useful in articlesdesigned to absorb large amounts of liquids, especiallyelectrolyte-containing liquids, such as in diapers and catamenialdevices.

[0158] The following nonlimiting examples illustrate the preparation ofthe multicomponent SAP fibers of the present invention. In the testresults set forth herein, the multicomponent SAP particles of thepresent invention were tested for absorption under no load (AUNL) andabsorption under load at 0.28 psi and 0.7 psi (AUL (0.28 psi) and AUL(0.7 psi)). Absorption under load (AUL) is a measure of the ability ofan SAP to absorb fluid under an applied pressure. The AUL was determinedby the following method, as disclosed in U.S. Pat. No. 5,149,335,incorporated herein by reference.

[0159] An SAP (0.160 g±0.001 g) is carefully scattered onto a140-micron, water-permeable mesh attached to the base of a hollowPlexiglas cylinder with an internal diameter of 25 mm. The sample iscovered with a 100 g cover plate and the cylinder assembly weighed. Thisgives an applied pressure of 20 g/cm² (0.28 psi) . Alternatively, thesample can be covered with a 250 g cover plate to give an appliedpressure of 51 g/cm² (0.7 psi). The screened base of the cylinder isplaced in a 100 mm petri dish containing 25 milliliters of a testsolution (usually 0.9% saline), and the polymer is allowed to absorb for1 hour (or 3 hours). By reweighing the cylinder assembly, the AUL (at agiven pressure) is calculated by dividing the weight of liquid absorbedby the dry weight of polymer before liquid contact.

EXAMPLE 1 Preparation of Poly(acrylic acid) Particles 0% Neutralized(Poly(AA) DN=0)

[0160] A monomer mixture containing acrylic acid (270 grams), deionizedwater (810 grams), methylene-bisacrylamide (0.4 grams), sodiumpersulfate (0.547 grams), and 2-hydroxy-2-methyl-1-phenyl-propan-1-one(0.157 grams) was prepared, then sparged with nitrogen for 15 minutes.The monomer mixture was placed into a shallow glass dish, then themonomer mixture was polymerized at an initiation temperature of 10° C.under 20 mW/cm² of UV light for about 12 to about 15 minutes. Theresulting poly(AA) was a rubbery gel.

[0161] The rubbery poly(AA) gel was cut into small pieces, then extrudedthree times through a KitchenAid Model K5SS mixer with meat grinderattachment. During extrusion, sodium metabisulfite was added to gel toreact with unreacted monomer. The extruded gel was dried in a forced-airoven at 145° C. for 90 minutes, and finally ground and sized throughsieves to obtain the desired particle size of about 180 to about 710 μm(microns).

[0162] This procedure provided a lightly crosslinked polyacrylic acidwith a degree of neutralization of zero (DN=0). The polyacrylid acid(DN=0) absorbed 119.5 g of 0.1 M sodium hydroxide (NaOH) per gram ofpolymer and 9.03 g synthetic urine per gram of polymer under a load of0.7 psi.

EXAMPLE 2 Preparation of a Crosslinked Poly(vinylamine) Resin Particles

[0163] To 100 g of an 8% by weight aqueous poly(vinylamine) solution wasadded about 2 mol % (0.66 g) of ethylene glycol diglycidyl ether(EGDGE). The resulting mixture was stirred for about 5 minutes todissolve the EGDGE, then the homogeneous mixture was placed in an oven,heated to about 60° C., and held for two hours to gel. The resulting gelthen was extruded three times, and dried to a constant weight at 60° C.The dried, lightly crosslinked poly(vinylamine) (poly(VAm)) then wascryogenically milled to form a granular material (about 180 to about 710μm). The crosslinked poly(VAm) absorbed 59.12 g/g of 0.1 M hydrochloricacid under no load, and 17.3 g/g of synthetic urine under a load of 0.7psi.

EXAMPLE 3 Preparation of Poly(acrylic acid) Fibers by Dry Spinning

[0164] A spinning solution was prepared by concentrating an aqueous 35%(w/w) solution of uncrosslinked poly(acrylic acid) (poly(AA)), molecularweight about 250,000, to 55% (w/w). To this solution was added EGDGE(0.5% to 5% mol/mol poly(AA)) and triethylamine (5% mol/mol poly(AA)),and the resulting mixture was mixed to produce a homogeneous spinningsolution. The viscosity of the spinning solution, at 55% (w/w), was13,000 cps (by Reverse Flow Viscometer, size 8, at 25° C.). The spinningsolution was placed in a Petri dish and fibers were drawn verticallyupwards to a rotating drum (diameter of 15.5 cm). The dry spinningapparatus is illustrated in FIG. 8. The pull off speed was about 54 rpmwith a filament draw length of 500 mm. The drawn fibers were curedeither by microwave using 720 watts (W) power (2 minutes for 5% EGDGE)or by a conventional fan-assisted oven at 60° C. (60 minutes for 5%EGDGE). The time needed to cure the fiber was dependent upon theconcentration of EGDGE. In the preparation of poly(AA) by dry spinning,the concentration of EGDGE in the spinning solution typically is about0.5 to about 5% (mol/mol poly(AA)). The addition of triethylamine as acure catalyst resulted in a faster cure, which occurred at a lowertemperature.

[0165] The resulting poly(AA) fibers were about 25 μm in diameter and0.71 denier (0.078 tex). The fibers absorbed about 69.9 g/g of 0.1 MNaOH at no load after 1 hour, and about 17.6 g/g of synthetic urine at0.28 psi after 1 hour.

EXAMPLE 4 Preparation of Poly(vinylamine) Fibers by Wet Spinning

[0166] A spinning solution was prepared by concentrating a 6% w/waqueous solution of poly(VAm) to 10% w/w poly(VAm) (molecular weightabout 190,000). EGDGE (0.025 mol %) was added to the poly(VAm) solution,and mixed to provide a homogeneous solution. The solution then washeated for about 30 minutes at about 40° C., and was spinnable. Theresulting spinning solution was introduced directly into a coagulationbath through a spinnerette submersed in a coagulating medium. Thecoagulation medium in the coagulation bath contained a mixture of EGDGE,typically 0.5% (w/w), and acetone. The concentration of EGDGE typicallyis about 0.5 to about 5% (w/w). The spinning solution was placed in asyringe fitted with a 23 gauge needle. The poly(VAm) was injected intothe coagulating medium at a flow rate of 0.02 ml/min, and the resultingpoly(VAm) was drawn off at a wind-up rate of 64 rpm. The diameter of thedrum was 12 cm. The wet spinning apparatus is illustrated in FIG. 9. Thepoly(VAm) fibers had a diameter of 28 μm and were 5.5 denier (0.61 tex).Curing was performed in an oven at 80° C. for 30 minutes. The poly(VAm)fiber absorbed 68.3 g/g (after 1 hour) and 73.5 g/g (after 3 hours) of0.1 M hydrochloric acid under no load, and 19.6 g/g (after 1 hour) undera load of 0.28 psi.

[0167] Poly(VAm) fibers also were produced from the identical spinningsolution using a dry-jet wet spinning technique. In this technique, thespinnerette was positioned above the coagulation bath and the fiberoriginally was spun in air, then pulled through the coagulation bath.

[0168] As illustrated above, the physical properties of poly(AA) permitdry spinning of the polymer. Poly(AA) has a high extensional viscositythat allows stringing of the polymer solution and drawing of filaments,or fibers, from a poly(AA) spinning solution. Poly(VAm) does not havethe physical properties necessary for dry spinning, and therefore issubjected to a wet spinning process. In the spinning of an acidic or abasic water-absorbing polymer, persons skilled in the art can determinewhether a dry spinning or a wet spinning process should be used based onthe properties of the resin.

EXAMPLE 5 Preparation of Twisted Rope Multicomponent SAP Fibers

[0169] A multicomponent SAP fiber of the present invention was preparedby twisting together a poly(AA) fiber of Example 3 and a poly(VAm) fiberof Example 4 to provide intimate contact between the acidic and basicwater-absorbing resins. After twisting the acidic and basicwater-absorbing fibers together, the resulting twisted rope fiber washeated in a 125° C. oven for about 10 to about 20 minutes. Twisted ropefibers containing a 50:50 mole ratio of poly(AA) of Example 3 andpoly(VAm) of Example 4 absorbed aqueous media as follows: Aqueous AUL¹⁾(g/g) AUL (g/g) Testing Medium (after 1 hr) (after 4 hr) Synthetic urine33.0⁴⁾ (20.2)³⁾ 35.7 (26.2) 30.4 36.4 0.9% saline 24.1 (19.6) 25.4(21.3) 23.9 24.6 Synthetic blood²⁾ 29.2 (24.1) 30.0 (26.1) 27.2 28.8

[0170] In another example, a twisted fiber containing a 2:1 mole rate ofpoly(VAm) fiber to poly(AA) fiber was prepared. This twisted fiber alsoexhibited excellent fluid adsorption properties. In addition, duringhydration of the twisted fiber, distinct entanglement of the fibers wasobserved.

[0171] In Example 5, the twisted rope was annealed after the fibers weretwisted together. However, annealing of the individual fibers, prior tobraiding, also can be performed, as well as annealing of the individualfibers followed by annealing of the twisted rope fiber.

[0172] Although Example 5 is directed to a single fiber of a poly(AA)and a single fiber of a poly(VAm) twisted together in the form of abraid, a twisted rope fiber of the present invention also encompassesembodiments wherein one or more poly(AA) fibers and one or morepoly(VAm) fibers are twisted together in the form of a braid.Accordingly, embodiments wherein one or a plurality of (e.g., 1 to 500)poly(AA) fibers twisted together with one or a plurality of (e.g., 1 to500) poly(VAm) fibers also are within the scope of the presentinvention.

[0173] In the twisted fiber embodiment, the mole ratio of basic resin toacidic resin is about 5:1 to about 1:5, and preferably about 3:1 toabout 1:3. To achieve the full advantage of the present invention, themole ratio is about 2:1 to about 1:2.

[0174] The effect of cure time and cure temperature on absorbency of a50:50 mole ratio twisted fiber of Example 5 also was examined. Theresults of this test are summarized in Table 1. TABLE 1 Effect of curetime and temperature on the absorbency of twisted fibers Time of cureTemp of AUL¹⁾ (g/g) AUL¹⁾ (g/g) (mins) cure (° C.) (after 1 hr) (after 3hr)  30  80 33.08 37.66  10 125 38.41 40.03  20 125 55.46 63.21  30 12533.53 36.80 120 125 29.28 32.11

[0175] The rate of absorption for the 50:50 mole ratio twisted fibers ofExample 5, cured at 125° C. for 20 minutes, was compared to OASIS™fibers, poly(VAm) fibers of Example 4, and poly(AA) fibers of Example 3.The results are summarized in FIG. 10. FIG. 10 shows that the twistedSAP fibers absorb more rapidly than poly(VAm) and poly(AA) fibers, andover time outperforms OASIS™ fibers.

[0176] A test also was performed to determine whether fiber lengthaffected absorption. The twisted fiber multicomponent SAP of Example 5,having a length of 5, 10, 20, and 40 mm, was compared to poly(AA)granules, OASIS™ fibers, and physical blends of poly(AA) and poly(VAm)fibers having a length 5, 10, 20, and 40 mm in length, for absorptionrate of synthetic urine under 0.28 psi pressure. Absorption improvedwith increasing fiber length up to 20 mm, then decreased at 40 mm. Thetwisted fiber multicomponent SAP outperformed the blend of poly(AA) andpoly(VAm) fibers.

[0177] A multicomponent SAP fiber of the present invention also can bein the form of a core of a first resin and a sheath, or shell, of asecond resin. This embodiment is illustrated in Examples 6 and 7.

EXAMPLE 6 Preparation of Multicomponent SAP Fibers Having a Poly(AA)Core and a Poly(VAm) Sheath

[0178] Poly(AA) fibers were prepared as set forth in Example 3. Thepoly(AA) fibers then were passed through a solution of poly(VAm) (10-20%solids like in Example 4). The resulting coated fiber then was passedthrough a coagulation bath containing EGDGE (0.5 w/w) and acetone. Theresulting core/sheath multicomponent SAP fibers were dried and cured ina fan-assisted oven at 60° C. for 1 hour. A typical core/sheathmulticomponent SAP fibers contained about 0.008 g of poly(AA) and 0.011g of poly(VAm), or a mole ratio of acrylic acid to vinylamine of 1:2.3.The multicomponent SAP fiber of Example 6 absorbed 18.2 g/g of syntheticurine after 60 minutes under a 0.7 psi load. In comparison, the poly(AA)fibers of Example 3 absorbed 8.4 g/g under identical conditions.

EXAMPLE 7 Preparation of Multicomponent SAP Fibers Having a Poly(VAm)Core and a Poly(AA) Sheath

[0179] An aqueous polyvinylamine solution (10% solids) was combined with0.025 mol % of EGDGE crosslinker. The resulting solution was mixed untilhomogeneous, and then allowed to crosslink lightly at 40° C. for 20minutes to form a spinning dope. The dope was injected directly into acoagulation bath containing EGDGE, typically in an amount of about 0.25%to about 1% based on a w/w % concentration. The coagulant in the bathwas a nonsolvent for poly(VAm), typically acetone. The poly(VAm) wasspun directly into the bath at a flow rate of 2.54 cm³/hr. The fiber wasproduced at a fast rate, with coagulation occurring initially from theoutside. The process started with the production of a skin. This type ofcoagulation produced a fiber morphology having voids within the core, asillustrated in FIGS. 11-13. The fiber was drawn through the bath, andupwards from the bath. On drawing the fiber from the coagulation bath,it was passed over an acetone soaked roller and then passed into acoating bath containing poly(AA) and EGDGE. This bath contained aconcentrated aqueous solution of poly(AA) (50-70 w/w %) diluted to about15% w/w % polyacrylic acid with a polar solvent, typically acetone. TheEGDGE was present at about 0.5 mol %. Passing the fiber through thisbath coated the core of poly(VAm) with a sheath of poly(AA). Afterpassing through this bath, the fiber was passed over a secondacetone-coated roller and into a doping bath containing 5 wt %triethylamine in acetone. After passing the fiber through this solution,the fiber was wound at a speed of about 50-60 rpm. The fibers thusproduced were removed from the roller and cured for 30 minutes at 125°C. The multicomponent SAP fibers were 25 denier (2.8 tex). Increasingthe cure time of the fibers at 125° C. up to 60 minutes or longer,resulted in a change in the morphology of the hydrated fibers. Thehydrated fiber gel was harder than hydrated fibers cured for only 20 to30 minutes. Upon removal of the fibers from the AUL test cell, thestructure fell apart and no longer resembled a mat.

[0180] The multicomponent SAP fibers of Example 7 were tested for anability to absorb artificial urine, artificial blood, and 0.9% saline.The test results are summarized below. Aqueous AUL (after 1 AUL (after 4Testing medium hour @ 0.7 psi) hour @ 0.7 psi) Synthetic urine 24.9 26.00.9% saline 19.3 24.4 Synthetic blood 20.5 22.5

[0181] Upon hydration, the fibers of Example 7 formed a mat-typestructure. On completion of the AUL test, the mat maintained itsintegrity, and it was possible to remove the mat as one piece. Incontrast, the twisted rope fiber of Example 5 fractured into itsindividual fiber components after hydration. Examination of the matproduced with the core-shell fiber of Example 7 revealed an openstructure with a very fibrous appearance. No free fluid was present onthe surface of the fibers. Accordingly, all of the fluid was containedwithin the structure of the fiber. It also was observed that as thecoating of poly(AA) increased, AUL values of 50 g/g were attained.

[0182] The fibers of Example 7 were tested to determine the effect ofcure time on the absorbency of the fibers under a 0.7 psi load. Foursamples were prepared identically, then subjected to a cure time of 1,3, 5, or 20 minutes, each at 125° C. The test results are summarized inTable 2, showing that an increased curing time improved the absorptionof synthetic urine. TABLE 2 Time of cure AUL (g/g) AUL (g/g) (mins)(after 1 hr) (after 3 hr)  1 16.9 17.6  3 17.6 18.9  5 18.9 20.0 20 29.029.5

[0183] The fibers of Example 7 also were prepared using an alternateprocedure wherein poly(VAm) fibers prepared in Example 4 were passedthrough a solution containing poly(AA), EGDGE (about 0.5 to about 5 mol%), and triethylamine (5 mol %). In different runs, the fibers weredried and cured either by microwave (720W) for 4 minutes, or by afan-assisted oven at 60° C. for 60 minutes. A typical core-sheath SAPfiber contained 0.16 g poly(VAm) and 0.16 g poly(AA), i.e., a mole ratioof poly(VAm) to poly(AA) of 2:1. This SAP fiber absorbed 26.8 g/g ofsynthetic urine under a load of 0.7 psi after 60 minutes. Under the sameconditions, poly(VAm) fibers absorbed 14.2 g/g of synthetic urine.

[0184] The following Examples 8-11 illustrate other embodiments of thepresent invention, in particular, embodiments wherein the fibercomprises microdomains of an acidic resin in a continuous phase of abasic resin, or vice versa.

EXAMPLE 8 Preparation of a Poly(VAm) Fiber Containing Microdomains ofPoly(AA)

[0185] To a poly(VAm) spinning solution prepared as set forth in Example4 was added finely milled poly(AA) fines (<20 μm diameter). The mixturewas stirred until a homogeneous solution was obtained (about 5 minutes).The spinning solution was spun into an EGDGE (about 0.5% to about 5%w/w)-acetone coagulation bath as in Example 4. The resulting fibers werecured in an oven at 60° C. for 60 minutes.

[0186] A typical multicomponent SAP fiber of Example 8 contained 5.54 gof poly(VAm) and 0.11 g of poly(AA), which is a mole ratio of poly(VAm)of poly(AA) of 6:1, and 2% w/w amount of EGDGE crosslinker. These fibersabsorbed 24.2 g/g synthetic urine after 1 hour under a load of 0.7 psi.An identical poly(VAm) fiber that is free of poly(AA) fines, absorbed12.1 g/g, under identical conditions.

EXAMPLE 9 Preparation of a Poly(AA) Fiber Containing Microdomains ofPoly(VAm)

[0187] To an aqueous poly(AA) solution prepared as set forth in Example3 was added finely milled poly(VAm) fines (<20 μm diameter). The mixturewas stirred until a homogeneous solution was obtained (about 5 minutes).The spinning solution was dry spun as described in Example 3. Theresulting fibers were cured in an oven at 60° C. for 60 minutes.

[0188] A typical multicomponent SAP fiber of Example 9 contained 0.13 gof poly(VAm) and 4.94 g of poly(AA), which is a mole ratio of poly(VAm)to poly(AA) of 1:12, and 0.5% w/w of EGDGE crosslinker. The fibers ofExample 9 absorbed 18.4 g/g of synthetic urine after 1 hour under a loadof 0.7 psi. An identical poly(AA) fiber that is free of poly(VAm) finesabsorbed 8.4 g/g, under identical conditions.

EXAMPLE 10

[0189] In a method identical to Example 9, VISCOMER™ was added to asolution of poly(VAm). VISCOMER™ is a commercially available poly(AA)from Chemdal Corporation, Palatine, Ill. VISCOMER™ has a molecularweight of about 4 million, and a particle size of less than 10 μm indiameter. The resulting spinning solution was spun into an EGDGE (fromabout 0.5 to about 5% w/w)-acetone coagulation bath as previouslydescribed. The resulting fibers were cured in an oven at 60° C.overnight.

[0190] A typical multicomponent SAP fiber of Example 10 contained a moleratio of poly(VAm) to poly(AA) of 1:1, and 0.5% w/w of EGDGEcrosslinker. The fibers of Example 10 absorbed 14.47 g/g of syntheticurine under a load 0.7 psi after 60 minutes.

EXAMPLE 11

[0191] In a method identical to Example 9, CARBOPOL™ was added to asolution of poly(VAm). CARBOPOL™ is a commercially available poly(AA)from BF Goodrich Co., Cleveland, Ohio. CARBOPOL™ has a molecular weightof about 400,000 to about 4,000,000, and a particle size of about 2 toabout 7 μm in diameter. The resulting spinning solution was spun into anEGDGE (about 0.5 to about 5% w/w)-acetone coagulation bath as previouslydescribed. The resulting fibers were cured in an oven at 60° C.overnight.

[0192] A typical multicomponent SAP particle of Example 10 contained a1:1 mole ratio of poly(VAm) to poly(AA), and 0.5% w/w of EGDGEcrosslinker. The fibers of Example 11 absorbed 17.5 g/g of syntheticurine under a load of 0.7 psi after 60 minutes.

[0193] The following Example 12 illustrates an embodiment whereinpoly(VAm) and poly(AA) fibers are coextruded.

EXAMPLE 12 Preparation of Multicomponent SAP Fibers by Coextrusion

[0194] Poly(VAm) fibers were prepared by the wet spinning methoddisclosed in Example 4. In parallel, poly(AA) fibers were prepared bythe dry spinning method disclosed in Example 3. The poly(AA) fibers werepassed through a heated chamber at 60° C., followed by coextrusion withthe poly(VAm) fibers. The coextruded SAP fibers were cured at 60° C. for1 hour.

[0195] A typical coextruded multicomponent SAP fiber of the presentinvention contains a 1:1 mole ratio of poly(VAm) to poly(AA). Thecoextruded fiber absorbed 28.1 g/g of synthetic urine under a load of0.7 psi after 60 minutes. In comparison, the poly(AA) fibers of Example3 absorbed 8.4 g/g and the poly(VAm) fibers of Example 4 absorbed 12.9g/g under identical conditions.

[0196] The following Example 13 illustrates surface treating amulticomponent SAP fiber of the present invention.

EXAMPLE 13 Surface Treating of Multicomponent SAP Fibers

[0197] The twisted rope SAP fibers of Example 5 were passed through asolution of propylene glycol and water (80:20 w/w) to coat the twistedfibers. The coated twisted fibers then were dried in a 125° C. oven for1 hour. The resulting surface crosslinked SAP fibers had a mole ratio ofpoly(AA) to poly(VAm) of 1:1, and a weight ratio of twisted fibers tosurface coating of 4.7:1. The surface crosslinked multicomponent SAPfibers absorbed 10.5 g/g of synthetic urine under a load of 0.7 psiafter 60 minutes.

[0198] The following tables contain absorption and retention data forthe multicomponent SAP fibers of the present invention, for individualpolymers present in the multicomponent SAP fibers, and for simpleadmixtures of the dry resins present in the multicomponent SAP fibers.The data shows a significant improvement in water absorption andretention for the present multicomponent SAP fibers containingmicrodomains of an acidic and/or basic resin polymers within eachparticle compared to the individual resins and a simple admixture of theindividual resins. The data in Tables 3-8 shows the improved ability ofmulticomponent SAP fibers of the present invention to absorb and retainan aqueous 0.9% saline solution. TABLE 3 AUL AUL (0.28 AUL (0.28 AULpsi, (0.7 psi, AUNL psi, (0.7 psi, AUNL SAP 1 hr.) 1 hr.) (1 hr.) 3 hr.)3 hr.) (3 hr.) Poly(DAEA) 9.6 8.1 23.9 13.5 9.3 24.2 alone¹⁾ PolyacrylicAcid 11.9 10.8 14.3 12.0 10.8 14.3 alone²⁾ SAP-1³⁾ 11.0 10.9 45.2 14.814.4 48.0 SAP-2⁴⁾ 12.5 9.6 26.7 18.9 13.1 30.1 SAP-3⁵⁾ 12.4 11.3 37.316.5 14.7 42.3 SAP-4⁶⁾ 20.1 17.2 28.6 24.7 20.7 34.1 SAP-5⁷⁾ 25.3 18.235.3 28.1 23 38.7 Multicomponent SAP-1⁸⁾    0⁹⁾ 23.7 16.3 41.6 26.9 2041.7   200 26.7 24.7 41.2 27.1 25.1 39.9   400 27.3 24.1 43.4 27.5 24.544.0   600 29.2 23.8 41.8 29.5 24.0 41.2   800 26.6 24.1 40.9 26.7 24.241.7 1,000 27.5 24.3 39.9 27.8 24.2 40.7 Multicomponent SAP-2¹⁰⁾  0⁹⁾26.3 15.4 40 26.9 17.3 39.4 400 26.5 20.5 39.3 27 22.4 40.3 600 27 18.340.2 27.1 20.7 40.6

[0199] TABLE 4 AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi, AUNL psi, (0.7psi, AUNL SAP 1 hr.) 1 hr.) (1 hr.) 3 hr.) 3 hr.) (3 hr.)Poly(DMAPMA)¹¹⁾ 10.2 8.6 18 11.4 10 18.3 Poly(DMAPMA)¹²⁾ 9.3 5.2 17.4 116.9 17.8 Polyacrylic acid¹³⁾ 11.9 10.8 14.3 12.0 10.8 14.3 SAP-6¹⁴⁾ 14.510.9 18.8 17.2 14.3 20.9 SAP-7¹⁵⁾ 14 12 38.7 17.9 15.7 43.6 SAP-8¹⁶⁾12.5 10.4 24.8 14.5 12.4 24.8 Multicomponent SAP-3¹⁷⁾  0⁹⁾ 28.8 15 41.631 17.5 41.5 100 27.4 24.2 38.8 27.1 23.6 38.8 200 27.3 24.2 39.8 25.823 39   400 26 23 37 25.2 22.5 36.4 600 25.1 22.3 37.1 24.7 21.3 36.1Multicomponent SAP-4¹⁸⁾  0⁹⁾ 31.9 11.6 44.2 31.8 15.7 44.9 200 27.6 24.337.8 27.5 23.4 38.1 400 27.5 23.7 37.4 27.2 23.1 38.8 MulticomponentSAP-5¹⁹⁾   0²⁰⁾ 23.6 12.9 37.9 25 14.4 38.5 1500 24.7 16.9 36.4 25.518.3 37.5

[0200] TABLE 5 AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi, AUNL psi, (0.7psi, AUNL SAP 1 hr.) 1 hr.) (1 hr.) 3 hr.) 3 hr.) (3 hr.)Poly(vinylamine) 14.2 14.4 21.4 15 14.3 23.4 alone SAP-9²¹⁾ 21.2 18.628.3 23.8 20.5 36.3 Multicomponent SAP-6²²⁾  0⁹⁾ 14.9 12.8 53.8 16.915.6 55.4 100 37.5 30.1 45.5 37.5 30.1 45.5 200 36.2 30.4 48.5 35.9 30.247.4 400 34.6 30.6 44.9 34.6 30.6 46.2

[0201] TABLE 6 Coextruded Multicomponent SAP Particle (60/40 weightratio poly(DAEA)/poly(AA) AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi,AUNL psi, (0.7 psi, AUNL Surface Treatment 1 hr.) 1 hr.) (1 hr.) 3 hr.)3 hr.) (3 hr.) 0 30.5 13.3 41.1 30.6 16.3 40.2 200 ppm EGDGE 31 27.740.2 30.8 27.3 39.9

[0202] TABLE 7 AUL AUL (0.28 AUL (0.28 AUL psi, (0.7 psi, AUNL psi, (0.7psi, AUNL SAP 1 hr.) 1 hr.) (1 hr.) 3 hr.) 3 hr.) (3 hr.) Poly(vinyl- 2116.1 31.2 22.4 18.0 32.7 quanidine) hydro- chloride alone MulticomponentSAP-7²³⁾  0⁹⁾ 18.8 12.7 40.6 21.2 15.3 46.8 200 22 19.2 33.5 23.5 20.337.4

[0203] TABLE 8 Coextruded Multicomponent SAP Particle (37.4/62.6 weightratio PEI/poly(AA)) Cross- AUL (0.28 AUL (0.7 AUL (0.28 AUL (0.7 PEI Gellinker psi, psi, AUNL (1 psi, psi, AUNL (3 (% Solids) Level²⁴⁾ 1 hr.) 1hr.) hr.) 3 hr.) 3 hr.) hr.) 20 1.0 23 19.5 32 24.3 20.8 34.9 10 1.520.1 16.2 28.4 22.4 18.1 31.9

[0204] To demonstrate that a multicomponent SAP fiber of the presentinvention can contain an acidic resin and/or a basic resin that ispartially neutralized, a series of tests was performed on multicomponentSAP particles containing 45% by weight poly(AA) and 55% by weightpoly(vinylamine). The multicomponent SAP particles were prepared in anidentical manner, but the percent neutralization of the poly(AA) andpoly(vinylamine) was changed. The various multicomponent SAP particleswere tested for an ability to absorb and retain synthetic urine, and theresults are summarized in Table 9. TABLE 9 % NeutralizedPoly(vinylamine)/ AUL AUL % Neutralized Surface (0.7 psi, (0.7 psi,Poly(AA) (by weight) Crosslinking 1 hr) 3 hr) 0/0 None 16.8 21.6  0/10None 13.4 16.9  0/25 None 12.6 16 10/0  None 37.2 37.7 25/0  None 24.425.3 10/10 None 19.2 24.3 25/25 None 19.8 19.3 50/50 None 11.9 13.8 0/0PG/H₂O ¹⁾ 43.3 47.6  0/10 PG/H₂O 34 36.9  0/25 PG/H₂O 14.4 17.4 10/0 PG/H₂O 30.9 31.4 25/0  PG/H₂O 24.1 25.3 10/10 PG/H₂O 39.3 41.2 25/25PG/H₂O 18.9 18.7 50/50 PG/H₂O 12.1 14.5

[0205] In another series of tests, the ratio of acidic water-absorbingresin to basic water-absorbing resin in the multicomponent SAP particleswas varied. In particular, Table 10 summarizes the AUNL data and the AULdata at different pressures for a series of multicomponent SAP particlescontaining poly(vinylamine) and poly(AA) over the range of 25% to 75% byweight. The multicomponent SAP particles used in this series of testswere multicomponent SAP particles containing 55% by weightpoly(vinylamine) and 45% by weight poly(acrylic acid). Allmulticomponent SAP particles used in the test were surface-crosslinkedwith 50 ppm EGDGE. The multicomponent SAP particles were tested for anability to absorb and retain synthetic urine. TABLE 10 Weight Ratio AULAUL AUL AUL AUL AUL AUL Poly (vinyl 0.28 0.7 1.4 0.28 0.7 1.4 0.28 AULAUL amine)/- psi psi psi AUNL psi psi psi AUNL psi 0.7 psi 1.4 psi AUNLPoly(AA) (1 hr) (1 hr) (1 hr) (1 hr) (3 hr) (3 hr) (3 hr) (3 hr) (17 hr)(17 hr) (17 hr) (17 hr) 25/75 41.3 36.6 53.6 41.2 36.6 54 39.1 33.3 52.330/70 46.3 42.2 58.7 46.4 42.8 59.6 43.1 38.7 58.4 35/65 43.6 38.5 54.444.2 39.5 54.8 42 35.8 54.3 40/60 52.1 44.3 63.9 53.7 46.5 66.7 51.743.2 65.2 45/55 50.4 46 61.1 51.4 47.4 63.2 47.3 41.9 61.9 50/50 52.2 4526 62.5 54.8 47.7 29 66.7 52.8 45.4 30.9 66.4 55/45 52.1 47.3 27.4 62.554.8 49.3 31.3 66.2 53.1 44.8 32.5 65.4 60/40 52.8 47 27.8 64.6 55.249.6 30.9 68 52.6 44 33 67.6 65/35 50 45.9 59.2 51.6 47.3 61.8 48.8 4161.4 70/30 47.5 43.1 57.4 48.3 43.8 59.4 43.5 37.2 56.7 75/25 43.9 39.353.6 43.9 39.2 54.8 38.9 31.2 51.4

[0206] In addition to an ability to absorb and retain relatively largeamounts of a liquid, it also is important for an SAP to exhibit goodpermeability, and, therefore, rapidly absorb the liquid. Therefore, inaddition to absorbent capacity, or gel volume, useful SAP fibers alsohave a high gel strength, i.e., the fibers do not deform after absorbinga liquid. In addition, the permeability or flow conductivity of ahydrogel formed when SAP fibers swell, or have already swelled, in thepresence of a liquid is extremely important property for practical useof the SAP fibers. Differences in permeability or flow conductivity ofthe absorbent polymer can directly impact on the ability of an absorbentarticle to acquire and distribute body fluids.

[0207] Many types of SAP particles exhibit gel blocking. “Gel blocking”occurs when the SAP particles are wetted and swell, which inhibits fluidtransmission to the interior of the SAP particles and between absorbentSAP particles. Wetting of the interior of the SAP particles or theabsorbent structure as a whole, therefore, takes place via a very slowdiffusion process, possibly requiring up to 16 hours for complete fluidabsorption. In practical terms, this means that acquisition of a fluidby the SAP particles, and, accordingly, the absorbent structure, such asa diaper, can be much slower than the rate at which fluids aredischarged, especially in gush situations. Leakage from an absorbentstructure, therefore, can occur well before the SAP particles in theabsorbent structure are fully saturated, or before the fluid can diffuseor wick past the “gel blocked” particles into the remainder of theabsorbent structure. Gel blocking can be a particularly acute problem ifthe SAP particles lack adequate gel strength, and deform or spread understress after the SAP particles swell with absorbed fluid.

[0208] Accordingly, an SAP particle can have a satisfactory AUL value,but will have inadequate permeability or flow conductivity to be usefulat high concentrations in absorbent structures. In order to have a highAUL value, it is only necessary that the hydrogel formed from the SAPparticles has a minimal permeability such that, under a confiningpressure of 0.3 psi, gel blocking does not occur to any significantdegree. The degree of permeability needed to simply avoid gel blockingis much less than the permeability needed to provide good fluidtransport properties. Accordingly, SAPs that avoid gel blocking and havea satisfactory AUL value can still be greatly deficient in these otherfluid handling properties.

[0209] Accordingly, an important characteristic of the multicomponentSAP fibers of the present invention is permeability when swollen with aliquid to form a hydrogel zone or layer, as defined by the Saline FlowConductivity (SFC) value of the SAP particles. SFC measures the abilityof an SAP to transport saline fluids, such as the ability of thehydrogel layer formed from the swollen SAP to transport body fluids. Amaterial having relatively high SFC value is an air-laid web of woodpulpfibers. Typically, an air-laid web of pulp fibers (e.g., having adensity of 0.15 g/cc) exhibits an SFC value of about 200×10⁻⁷ cm³ sec/g.In contrast, typical hydrogel-forming SAPs exhibit SFC values of 1×10⁻⁷cm³ sec/g or less. When an SAP is present at high concentrations in anabsorbent structure, and then swells to form a hydrogel under usagepressures, the boundaries of the hydrogel come into contact, andinterstitial voids in this high SAP concentration region becomegenerally bounded by hydrogel. When this occurs, the permeability orsaline flow conductivity properties in this region is generallyindicative of the permeability or saline flow conductivity properties ofa hydrogel zone formed from the SAP alone. Increasing the permeabilityof these swollen high concentration regions to levels that approach oreven exceed conventional acquisition/distribution materials, such aswood pulp fluff, can provide superior fluid handling properties for theabsorbent structure, thus decreasing incidents of leakage, especially athigh fluid loadings.

[0210] Accordingly, it would be highly desirable to provide SAPparticles having an SFC value that approaches or exceeds the SFC valueof an air-laid web of wood pulp fibers. This is particularly true ifhigh, localized concentrations of SAP particles are to be effectivelyused in an absorbent structure. High SFC values also indicate an abilityof the resultant hydrogel to absorb and retain body fluids under normalusage conditions.

[0211] The SFC value of the present multicomponent SAP particles aresubstantially improved over the SFC value for a standard poly(AA) SAP,as illustrated in the data summarized in Table 11. A method fordetermining the SFC value of SAP particles is set forth in Goldman etal. U.S. Pat. No. 5,599,335, incorporated herein by reference. TABLE 11Sample 1 Sample 2 (Control)¹⁾ (Comparative)²⁾ Sample 3³⁾ Sample 4⁴⁾Sample 5⁵⁾ Sample 6⁶⁾ Sample 7⁷⁾ Time AUL AUL AUL AUL AUL AUL AUL (min)0.7 psi 0.7 psi 0.7 psi 0.7 psi 0.7 psi 0.7 psi 0.7 psi 0 0 0 0 0 0 0 05 25.3 14.8 26 26.3 17.8 19.3 13.6 10 30.7 20.9 33.2 34.5 23.4 20.4 16.215 32.1 25.1 37.9 38.8 26.3 21 17.4 30 33.8 31.2 43.3 44.1 29.9 20.817.6 45 34.2 34.3 45.8 45.6 31.8 21.6 19.3 60 34.5 36.4 47.6 46.2 32.421.7 20.1 120 35.2 40 49.1 47.6 33.6 22.3 20.5 180 35.2 42.3 49.7 4835.6 22.8 21.7 SFC⁸⁾ 15 115 368 685 707 534 930

[0212] The data summarized in Table 11 shows a substantial improvementin AUL at 0.7 psi and SFC for multicomponent SAP particles in comparisonto a control SAP and a comparative dry blend of SAP particles.Accordingly, a present multicomponent SAP fiber has an SFC value of atleast about 150×10⁻⁷ cm³ sec/g, and preferably at least about 250×10⁻⁷cm³ sec/g. To achieve the full advantage of the present invention, theSFC value is at least about 350×10⁻⁷ cm³ sec/g, and can range to greaterthan 1000×10⁻⁷ cm³ sec/g.

[0213] The present multicomponent SAP particles also exhibit excellentdiffusion of a liquid through and between the particles. Diffusion ismeasured in a PUP capacity test, which is similar to the AUL test, butthe SAP particles are allowed to absorb a fluid on demand. The PUP testis designed to illustrate absorption kinetics of an SAP particle. It isexpected that a multicomponent SAP fiber of the present invention has aninitial PUP capacity rate of at least 50 g/g/hr^(½), and preferably atleast 70 g/g/hr^(½). To achieve the full advantage of the presentinvention, the multicomponent SAP fibers have an initial PUP capacityrate of greater than 90 g/g/hr^(½), and preferably greater than 100g/g/hr^(½).

[0214] In another test, the free swell rate (FSR) of a presentmulticomponent SAP particle was compared to the FSR of a standardpoly(AA) SAP and 55/45 weight ratio of poly(vinylamine)/poly(acrylicacid) dry particle blend. The FSR test, also known as a lockup test, iswell known to persons skilled in the art.

[0215] The present multicomponent SAP particles had an FSR (in g/g/sec)of 0.49 and 0.48, for 55/45 weight ratio multicomponent SAP particlesmade in a KitchenAid mixer and a Brabender extruder, respectively. Incomparison, a dry blend had an FSR of 0.10 and a standard neutralizedpoly(AA) had an FSR or 0.32. Multicomponent SAP particles of the presentinvention, therefore, have an FSR of greater than 0.35, preferablygreater than 0.40, and most preferably greater than 0.45. These datafurther show the improved ability of the present SAP particles to absorband retain larger amounts of an electrolyte-containing liquid quickly.

[0216] The multicomponent SAP fibers also can be mixed with particles ofa second water-absorbing resin to provide an SAP material havingimproved absorption properties. The second water-absorbing resin can bean acidic water-absorbing resin, a basic water-absorbing resin, or amixture thereof. The SAP material comprises about 10% to about 90%, andpreferably about 25% to about 85%, by weight, multicomponent SAP fibersand about 10% to about 90%, and preferably, about 25% to about 85%, byweight, particles of the second water-absorbing resin. More preferably,the SAP material contains about 30% to about 75%, by weight,multicomponent SAP fibers. To achieve the full advantage of the presentinvention, the SAP material contains about 35% to about 75%, by weight,the multicomponent SAP fibers.

[0217] The second water-absorbing resin can be any of the previouslydiscussed acidic resins used in the preparation of a multicomponent SAP.The second water-absorbing resin, either acidic or basic, can beunneutralized (DN=0), partially neutralized (O<DN<100), or completelyneutralized (DN=100). A preferred acidic water-absorbing resin used asthe second resin is polyacrylic acid, preferably partially neutralizedpolyacrylic acid, e.g., DN about 50%, and preferably about 70% up toabout 100%. The second water-absorbing resin also can be any of thepreviously discussed basic resins used in the preparation of amulticomponent SAP. Preferred basic water-absorbing resins used as thesecond resin are poly(vinylamine) or apoly(dialkylaminoalkyl(meth)acrylamide. Blends of acidic resins, orblends of basic resins, can be used as the second water-absorbing resin.Blends of an acidic resin and a basic resin also can be used as thesecond water-absorbing resin.

[0218] To illustrate the improved absorption properties demonstrated byan SAP material comprising multicomponent SAP particles and particles ofa second water-absorbing resin, mixtures of multicomponent SAP particlesand partially neutralized (DN=70) polyacrylic acid (poly(AA)) particleswere prepared. As used here and throughout the specification poly(AA)(DN=70) refers to a standard, commercial poly(AA) neutralized about 70%to about 80%, and poly(AA) (DN=0) refers to unneutralized poly(AA). Themulticomponent SAP particles contain microdomains of poly(vinylamine)dispersed in poly(AA) (DN=0). The poly(vinylamine)/poly(AA) weight ratioof the multicomponent SAP particles was 55/45. The resulting SAPmaterial was tested for an ability to absorb synthetic urine under loadat 0.7 psi, in accordance with the previously described method. Theresults are summarized below: AUL 0.7 psi AUL 0.7 psi SFC (×10⁻⁷ wtratio ¹⁾ (1 hr.) (3 hr.) cm³ sec/g) 100/0  26.7 27.1 14 75/25 30.2 30.726 50/50 36.7 37.7 72 25/75 40.8 42.6 189   0/100 43.0 46.4 787 

[0219] The data presented above shows a substantial improvement inabsorption properties achieved by an SAP material comprising a blend ofmulticomponent SAP particles and particles of a second water-absorbingresin over conventional, partially neutralized poly(AA).

[0220] The following Examples 14-17 show SAP materials containingpresent multicomponent SAP fibers and a second water-absorbing resin.

EXAMPLE 14

[0221] The core-sheath multicomponent SAP fibers of Examples 6 and 7,individually, were admixed with a commercial SAP, i.e., ASAP2300™granules, a 75%-80% neutralized poly(AA) available from Chemdal Corp.,Palatine, Ill., until a homogeneous mixture resulted. The resultingmixtures were about 50:50 (w/w) of fibers of Examples 6 or 7 andASAP2300™.

[0222] A typical mixture contained 0.052 g of fiber of Example 6 and0.050 g of ASAP2300™. The SAP material of Example 14 absorbed 29.7 g/gof synthetic urine after 1 hour under a load of 0.7 psi. In comparison,the fibers of Example 6 absorbed 18.2 g/g and ASAP2300™ absorbed 34.0g/g, under the identical conditions.

EXAMPLE 15

[0223] Similar to Example 14, the fibers of Examples 6 and 7,individually, were admixed with OASIS™ fibers. A typical formulationcontained 0.051 g of fibers of Example 7 and 0.050 g of OASIS™, i.e., a50:50 (w/w) ratio. The SAP material of Example 15 absorbed 20.1 g/g ofsynthetic urine after 1 hour under a load of 0.7 psi. In comparison, theOASIS™ fibers absorbed 18.9 g/g and the fibers of Example 7 absorbed26.8 g/g.

EXAMPLE 16

[0224] Similar to Examples 14 and 15, the coextruded fibers of Example12 were admixed with ASAP2300™, i.e., a 50:50 (w/w) ratio. The SAPmaterial of Example 16 absorbed 24.9 g/g of synthetic urine after 1 hourunder a load of 0.7 psi. In comparison, the fibers of Example 12absorbed 28.1 g/g and the ASAP2300™ granules absorbed 34.0 g/g, underidentical conditions.

EXAMPLE 17

[0225] Similar to Examples 14-16, the coextruded fibers of Example 12were admixed with OASIS™ fibers. A typical formulation contained 0.05 gof the fibers of Example 12 and 0.051 g of OASIS™ fibers, i.e., a 50:50(w/w) ratio. The SAP material of Example 17 absorbed 16.0 g/g ofsynthetic urine after 1 hour under a load of 0.7 psi. In comparison, thefibers of Example 12 absorbed 28.1 g/g and the OASIS™ fibers absorbed18.9 g/g, under identical conditions.

EXAMPLE 18

[0226] Similar to Examples 14-17, the twisted rope SAP fibers of Example5 were admixed with ASAP2300™ granules. A typical formulation contained0.07 g of the twisted rope SAP fibers and 0.11 g of ASAP2300™, i.e., a40:60 (w/w) ratio. The SAP material of Example 18 absorbed 21.8 g/g ofsynthetic urine after 1 hour under a load of 0.7 psi. In comparison, thetwisted rope SAP fibers of Example 5 absorbed 16.9 g/g and ASAP2300™absorbed 34.0 g/g under identical conditions.

EXAMPLE 19

[0227] Similar to Examples 14-18, the twisted rope SAP fibers of Example5 were admixed with OASIS™ fibers. A typical formulation contained 0.070g of the twisted rope fibers and 0.067 g of the OASIS™ fibers, i.e., a50:50 (w/w) ratio. The SAP material of Example 19 absorbed 14.4 g/g ofsynthetic urine after 1 hour under a load of 0.7 psi. In comparison, thetwisted rope fibers of Example 5 absorbed 16.9 g/g and the OASIS™ fibersabsorbed 18.9 g/g, under identical conditions.

EXAMPLE 20 Mixed Bed Fiber

[0228] A 50:50 mixture, by weight, of poly(acrylic acid) fibers andpoly(vinylamine) fibers was prepared by admixing the fibers. Thepoly(AA) and poly(VAm) fibers were produced as described in Examples 3and 4, respectively, and were in the uncured state. The fiber mixturethen was passed through a circular core former, which directs the fibermixture through a sieve and collects the fiber mixture on paper, whileunder a vacuum, to form a mat. The mat thus formed then was cured, orannealed, for 60 minutes at 125° C. The cured mat was tested forabsorbency under a 0.7 psi load, and absorbed 37.6 g/g of syntheticurine after 1 hour and 42 g/g after 4 hours.

[0229] In an alternative route, the poly(AA) and poly(VAm) fibers werecured first, either prior to admixing or after admixing, and then thecured fibers were passed through a core former as above. After a finalcure of 60 minutes at 125° C., the fiber mat absorbed 32.9 g/g (ofsynthetic urine) after 1 hour and 35.3 g/g after 4 hours in an AUL test(under 0.7 psi).

[0230] The hydrated mats of Example 20 had very good structuralintegrity and retained their shape after being removed from the AULsample pot. The surface of the mat was relatively dry. The hydrated matsdid not disintegrate and did not sag to an appreciable degree.

[0231] To further demonstrate the improved absorption properties of thepresent multicomponent SAP fibers, or an SAP material containing thepresent SAP fibers, the multicomponent SAP fibers and SAP materials werecompared to physical blends of fibers and physical blends of a fiber anda granule. The comparative physical blends did not containmulticomponent SAP fibers of the present invention. The following Table12 summarizes the results of comparative tests on twenty samples,including fibers and SAP materials of the present invention andcomparative samples. The tested samples have the following compositions:Test Sample Composition  1 Physical mix¹⁾ of amine fibers of Example 4and acid fibers of Example 3 (comparative)  2 Physical mix of aminefibers of Example 4 and poly(AA) granules of Example 1 (comparative)  3Physical mix of amine granules of Example 2 and acid fibers of Example 3(comparative)  4 Multicomponent SAP fiber of Example 5  5 Physical mixof Test Sample 1 and OASIS ™ fibers (comparative)  6 Physical mix ofTest Sample 1 and ASAP2300 ™ granules (comparative)  7 Physical mix ofamine fibers of Example 4 and reprotonated OASIS ™ fibers (comparative) 8 Poly(VAm) granules of Example 2 blended with reprotonated OASIS ™fibers (comparative)  9 SAP material of Example 14 10 SAP material ofExample 15 11 SAP material of Example 16 12 SAP material of Example 1713 Multicomponent SAP fibers of Example 6 14 Multicomponent SAP fibersof Example 7 15 Multicomponent SAP fibers of Example 12 16Multicomponent SAP fibers of Example 9 17 Multicomponent SAP fibers ofExample 8 18 Multicomponent SAP fibers of Example 10 19 MulticomponentSAP fibers of Example 11 20 Multicomponent SAP fibers of Example 13

[0232] TABLE 12 Sample¹⁾  1 Absorption under 0.7 psi load for 2:1 mix -14.1 g/g (1 hour)  2 Absorption under 0.7 psi load for 2:1 mix - 20.6g/g (1 hour)  3 Absorption under 0.7 psi load for 1:1 mix - 32.0 g/g (1hour)  4 Absorption under 0.7 psi load for 2:1 mix - 13.7 g/g (1 hour) 5 Absorption under 0.7 psi load for 1:1 mix - 14.3 g/g (1 hour)  6Absorption under 0.7 psi load for 1:1 MIX - 21.8 g/g (1 hour)  7Absorption after 1 hour under a 0.7 psi load was 5 g/g fiber/fiber.There was no increase after 3 hours.  8 Absorption after 1 hour under0.7 psi was 10.6 g/g, increasing to 17.5 g/g after 3 hours.  9Absorption after 1 hour under 0.7 psi was 29.6 g/g, increasing to 31.7g/g after 3 hours. 10 Absorption after 1 hour under 0.7 psi was 20.1g/g, increasing to 22.5 g/g after 3 hours. 11 Absorption after 1 hourunder 0.7 psi was 24.8 g/g, increasing to 27.7 g/g after 3 hours. 12Absorption after 1 hour under 0.7 psi was 16.0 g/g, increasing to 19.8g/g after 3 hours. 13 Absorption after 3 hours under 0.7 psi was 21.8g/g. 0 load = 33 g/g after 3 hours. 14 Absorption after 3 hours under0.7 psi was 32.8 g/g. 0 load = 28.8 g/g after 3 hours. 15 Absorptionafter 1 hour under 0.7 psi was 28.1 g/g, increasing to 38.7 g/g after 3hours. 16 Absorption after 3 hours under 0.7 psi was 22.5 g/g. 0 load =44.6 g/g after 3 hours. 17 Absorption after 3 hours under 0.7 psi was24.4 g/g. 0 load = 23.1 g/g after 3 hours. 18 Absorption after 3 hoursunder 0.7 psi was 16.34 g/g. 0 psi = 9.12 g/g. 19 Absorption after 3hours under 0.7 psi was 22.74 g/g. 0 psi = 20.37 g/g. 20 Absorptionafter 1 hour under 0.7 psi was 10.4 g/g, increasing to 14.2 g/g after 3hours.

[0233] A present SAP material has an SFC of greater than 15×10⁻⁷ cm³sec/g, and typically greater than 20×10⁻⁷ cm³ sec/g. Preferredembodiments have an SFC about 30×10⁻⁷ cm³ sec/g or greater, for example,up to about 800×10⁻⁷ cm³ sec/g. In particular, an SAP materialcontaining 25% multicomponent SAP particle and 75% poly(AA)(DN=70)particles has an SFC of 34.4 cm³ sec/g. A present SAP material alsodemonstrates an improved initial PUP capacity rate of 45.5 g/g 1 hr^(½)for the superabsorbent material. A standard poly(AA) (DN=70) has aninitial PUP capacity rate of 40.7 g/g 1 hr^(½).

[0234] In particular, multicomponent SAP fibers of Example 7 were testedfor permeability using the SFC test. Analysis was performed on a 0.1 gtest sample under an applied load of 0.3 psi. For synthetic urine, thefibers of Example 7 exhibited an SFC of 603×10⁻⁷ cm³ sec/g. Similarly,for 0.9% saline and artificial blood, the fibers of Example 7 exhibitedan SFC of 32 and 4.8 cm³ sec/g, respectively.

[0235] The present multicomponent SAP fibers and superabsorbentmaterials containing multicomponent SAP fibers, (a) have an improvedability to absorb liquids faster, (b) have a better liquid diffusionrate, and (c) have an improved ability to absorb and retain liquids. Thepresent SAP fibers and SAP materials, therefore, are useful indisposable diapers, adult incontinence products, and catamenial devices,for example.

[0236] In particular, present day diapers generally consist of atopsheet made from a nonwoven material that is in contact with the skinof the wearer, an acquisition layer below (i.e., opposite the skin ofwearer) the topsheet, a core that is below the acquisition layer, and abacksheet below the core. This construction is well known in theindustry. The improvements provided by present multicomponent SAPfibers, or superabsorbent material, may permit an acquisition layer tobe omitted from a disposable diaper.

[0237] In addition, additional test samples, similar to Example 20, wereprepared and tested for an ability to absorb synthetic urine. The mixedbed fiber mats contained a weight ratio of either 60/40, 50/50, or 30/70poly(vinylamine) to poly(acrylic acid), and were prepared identically asset forth above in Example 20. The mixed bed fiber mats were annealed at125° C. for a time period ranging from 10 to 60 minutes. The ability ofthe mixed bed fibers to absorb synthetic urine is summarized in Table13. TABLE 13 Weight Ratio of Cure Condi- AUL Load 1 hr 4 hr PVAm to PAAFibers tions (psi) (g/g) (g/g) 50/50 125° C. 10 mins 0   68.71 65.20 0.28 34.64 46.28 0.7 32.96 45.13 125° C. 20 mins 0   73.57 68.40  0.2846.68 56.43 0.7 37.59 44.35 125° C. 30 mins 0   66.73 66.35  0.28 40.2537.20 0.7 36.81 39.16 125° C. 45 mins 0   62.29 59.03  0.28 41.83 39.600.7 31.41 36.75 125° C. 60 mins 0   66.53 61.97  0.28 43.54 47.22 0.736.05 37.39 30/70 125° C. 10 mins 0   53.82 47.51  0.28 41.23 48.77 0.727.48 39.10 125° C. 20 mins 0   56.19 50.67  0.28 34.77 42.56 0.7 32.3140.03 125° C. 30 mins 0   51.85 43.58  0.28 34.24 32.73 0.7 27.39 32.00125° C. 45 mins 0   49.77 45.10  0.28 37.34 44.00 0.7 32.31 31.58 125°C. 60 mins 0   48.75 42.39  0.28 34.34 36.47 0.7 52.59 57.73 60/40 125°C. 10 mins 0.7 30.12 34.59 125° C. 20 mins 0.7 37.52 36.81 125° C. 30mins 0.7 34.74 35.04 125° C. 45 mins 0.7 33.76 34.57 125° C. 60 mins 0.735.96 38.25

[0238] The mixed fibers of Example 20, and the mixed bed fibers testedin Table 13, showed excellent structural integrity after hydration bysynthetic urine, i.e., the mat of mixed bed fibers can be lifted withoutdisintegrating.

[0239] In addition, a significant improvement in liquid absorption, bothwith respect to kinetics and retention, are expected if the standardpoly(AA)(DN=70) presently used in diaper cores is completely replaced bymulticomponent SAP fibers, or is replaced by a superabsorbent materialof the present invention, i.e., a composition containing multicomponentSAP fibers and a second water-absorbing resin, such as poly(AA)(DN=70).

[0240] The improved results demonstrated by the present invention alsopermit the thickness of the diaper core to be reduced. Typically, corescontain 50% or more fluff or pulp to achieve rapid liquid absorptionwhile avoiding problems like gel blocking. Cores which containmulticomponent SAP fibers acquire liquids sufficiently fast to avoidproblems, like gel blocking, and, therefore, the amount of fluff or pulpin the core can be reduced, or eliminated. A reduction in the amount ofthe low-density fluff results in a thinner core, and, accordingly, athinner diaper.

[0241] Therefore, a diaper core can contain at least 50% of an SAP,preferably at least 75% of an SAP, and up to 100% of an SAP. In variousembodiments, the presence of a fluff or pulp is no longer necessary, ordesired. In each case, the SAP in the core contains multicomponent SAPfibers, in an amount of about 15% to 100% of the SAP. The remaining SAPcan be a second water-absorbing resin, either basic or acidic. Thesecond water-absorbing resin preferably is not neutralized, but can havea degree of neutralization up to 100%. The multicomponent SAP fibers canbe admixed with particles of a second water-absorbing resin forintroduction into a diaper core. Alternatively, a diaper core cancontain zones of multicomponent SAP fibers and zones of a secondwater-absorbing resin.

[0242] In addition to a thinner diaper, the present invention alsoallows an acquisition layer to be omitted from the diaper. Theacquisition layer in a diaper typically is a nonwoven or fibrousmaterial, typically having a high degree of void space, or “loft,” thatassists in the initial absorption of a liquid. Cores containingmulticomponent SAP fibers can acquire liquid at a sufficient rate suchthat diapers free of an acquisition layers are practicable.

[0243] Many modifications and variations of the invention ashereinbefore set forth can be made without departing from the spirit andscope thereof and, therefore, only such limitations should be imposed asare indicated by the appended claims.

What is claimed is:
 1. A multicomponent superabsorbent fiber comprising:(a) a core comprising at least one basic water-absorbing resin and (b) asheath comprising at least one acidic water-absorbing resin which formsa layer surrounding and in contact with the core.
 2. The fiber of claim1 wherein the basic resin comprises a strong basic resin, a weak basicresin, or a mixture thereof, and the acidic resin comprises a strongacidic resin, a weak acidic resin, or a mixture thereof.
 3. The fiber ofclaim 1 having a weight ratio of acidic resin to basic resin of about95:5 to about 5:95.
 4. The fiber of claim 1 wherein the core contains atleast one microdomain of at least one acidic resin.
 5. The fiber ofclaim 1 wherein the sheath contains at least one microdomain of at leastone basic resin.
 6. The fiber of claim 1 wherein the fiber is elongatedand acicular.
 7. The fiber of claim 6 wherein the fiber is in the shapeof a cylinder having a diameter of about 10 μm to about 1 mm and alength of about 1 mm to about 100 mm.
 8. The fiber of claim 6 whereinthe fiber is in the shape of a filament having a length diameter ratioof about 500 to about 10,000:1.
 9. The fiber of claim 1 wherein thefiber is annealed at a temperature of about 65° C. to about 150° C. forabout 20 minutes to about 16 hours.
 10. The fiber of claim 1 wherein thefiber is surface crosslinked with up to about 10,000 ppm of a surfacecrosslinking agent.
 11. The fiber of claim 10 wherein the surfacecrosslinking agent is selected from the group consisting of apolyhydroxy compound, a metal salt, a quaternary ammonium compound, amultifunctional epoxy compound, an alkylene carbonate, a polyaziridine,a haloepoxy, a polyamine, a polyisocyanate, and mixtures thereof. 12.The fiber of claim 1 wherein the basic resin has about 75% to 100% basicmoieties present in a free base form.
 13. The fiber of claim 1 whereinthe basic resin is lightly crosslinked.
 14. The fiber of claim 1 whereinthe basic resin is selected from the group consisting of apoly(vinylamine), a poly(dialkylaminoalkyl (meth)acrylamide), a polymerprepared from the ester analog of an N-(dialkylamino(meth)acrylamide), apolyethylenimine, a poly(vinylguanidine), a poly(allylguanidine), apoly(allylamine), a poly(dimethyldialkylammonium hydroxide), aguanidine-modified polystyrene, a quaternized polystyrene, a quaternizedpoly(meth)acrylamide or ester analog thereof, poly(vinylalcohol-co-vinylamine), and mixtures thereof.
 15. The fiber of claim 1wherein the acidic resin contains a plurality of carboxylic acid,sulfonic acid, sulfuric acid, phosphonic acid, or phosphoric acidgroups, or a mixture thereof.
 16. The fiber of claim 1 wherein theacidic resin has about 75% to 100% acid moieties present in the freeacid form.
 17. The fiber of claim 1 wherein the acidic resin is lightlycrosslinked.
 18. The fiber of claim 1 wherein the acidic resin isselected from the group consisting of polyacrylic acid, a hydrolyzedstarch-acrylonitrile graft copolymer, a starch-acrylic acid graftcopolymer, a saponified vinyl acetate-acrylic ester copolymer, ahydrolyzed acrylonitrile polymer, a hydrolyzed acrylamide copolymer, anethylene-maleic anhydride copolymer, an isobutylene-maleic anhydridecopolymer, a poly(vinylphosphonic acid), a poly(vinylsulfonic acid), apoly(vinylphosphoric acid), a poly(vinyl-sulfuric acid), a sulfonatedpolystyrene, a poly(aspartic acid), a poly(lactic acid), and mixturesthereof.
 19. The fiber of claim 1 wherein the basic resin comprises apoly(vinylamine), a poly(dialkylaminoalkyl (meth)acrylamide), apoly(vinylguanidine), a polyethylenimine, or a mixture thereof, and theacidic resin comprises poly(acrylic acid).
 20. The fiber of claim 19wherein the poly(dialkylaminoalkyl (meth)acrylamide) comprisespoly(dimethylaminoethyl acrylamide), poly(dimethylaminopropylmethacrylamide), or a mixture thereof.
 21. The fiber of claim 19 whereinthe poly(acrylic acid) resin further contains strong acid moieties. 22.The fiber of claim 1 wherein the core has voids.
 23. An articlecomprising a core containing a superabsorbent polymer, said corecomprising about 1% to 100% by weight of a multicomponent superabsorbentfiber of claim
 1. 24. A method of absorbing an aqueous medium comprisingcontacting the medium with a plurality of fibers of claim
 1. 25. Amethod of claim 24 wherein the aqueous medium contains electrolytes. 26.A method of claim 25 wherein the electrolyte-containing aqueous mediumis selected from the group consisting of urine, saline, menses, andblood.
 27. A superabsorbent material comprising: (a) multicomponentsuperabsorbent fibers of claim 1, and (b) particles of a secondwater-absorbing resin selected from the group consisting of an acidicwater-absorbing resin, a basic water-absorbing resin, and mixturesthereof.
 28. The superabsorbent material of claim 27 wherein themulticomponent superabsorbent fibers are present in an amount of about10% to about 90%, by weight, of the material.
 29. The superabsorbentmaterial of claim 27 wherein the multicomponent superabsorbent fibersare 0% to 25% neutralized, and the second water-absorbing resin is 0% to100% neutralized.
 30. The superabsorbent material of claim 27 whereinthe second water-absorbing resin comprises an acidic water-absorbingresin.
 31. A multicomponent superabsorbent fiber comprising: (a) a corecomprising at least one acidic water-absorbing resin and (b) a sheathcomprising at least one basic water-absorbing resin which forms a layersurrounding and in contact with the core.
 32. The fiber of claim 31wherein the fiber is surface crosslinked with up to about 10,000 ppm ofa surface crosslinking agent.
 33. The fiber of claim 32 wherein thesurface crosslinking agent is selected from the group consisting of (a)a dihalide or a disulfonate ester having the formula Y—(CH₂)_(p)—Y,wherein p is an integer 2 to 12 and Y, independently, is halo, tosylate,mesylate, an alkyl sulfonate ester, or an aryl sulfonate ester; (b) amultifunctional aziridine; (c) a multifunctional aldehyde, and acetalsand bisulfites thereof; (d) a halohydrin; (e) a multifunctional epoxycompound; (f) a multifunctional carboxylic acid containing 2 to 12carbon atoms, and methyl and ethyl esters, acid chlorides, andanhydrides derived therefrom; (g) an organic titanate; (h) a melamineresin; (i) a hydroxymethyl urea; (j) a multifunctional isocyanate; and(k) mixtures thereof.
 34. The fiber of claim 31 wherein the particle isannealed at a temperature of about 65° C. to about 150° C. for about 20minutes to about 16 hours.
 35. The fiber of claim 31 wherein the corecontains at least one microdomain of at least one basic resin.
 36. Thefiber of claim 31 wherein the sheath contains at least one microdomainof at least one acidic resin.
 37. An article comprising a multicomponentsuperabsorbent fiber of claim
 31. 38. A method of absorbing an aqueousmedium comprising contacting the medium with a plurality of fibers ofclaim
 31. 39. A superabsorbent material comprising: (a) multicomponentsuperabsorbent fibers of claim 31, and (b) particles of a secondwater-absorbing resin selected from the group consisting of an acidicwater-absorbing resin, a basic water-absorbing resin, and mixturesthereof.
 40. The superabsorbent material of claim 39 wherein themulticomponent superabsorbent fibers are 0% to 25% neutralized, and thesecond water-absorbing resin is 0% to 100% neutralized.
 41. Thesuperabsorbent material of claim 39 wherein the second water-absorbingresin comprises an acidic water-absorbing resin.
 42. A multicomponentsuperabsorbent fiber comprising: (a) one or more first fibers comprisingan acidic resin, and (b) one or more second fibers comprising a basicresin, wherein the first and second fibers are twisted together in theform of a braid.
 43. The fiber of claim 42 wherein the first fibercontains at least one microdomain of at least one basic resin.
 44. Thefiber of claim 42 wherein the second fiber contains at least onemicrodomain of at least one acidic resin.
 45. The fiber of claim 42wherein the fiber is annealed at a temperature of about 65° C. to about150° C. for about 20 minutes to about 16 hours.
 46. The fiber of claim42 wherein the first fiber, the second fiber, both the first and secondfibers are surface crosslinked with up to about 10,000 ppm of a surfacecrosslinking agent.
 47. The fiber of claim 42 wherein the fiber issurface crosslinked with up to about 10,000 ppm of a surfacecrosslinking agent.
 48. An article comprising a core containing asuperabsorbent polymer, said core comprising about 1% to 100% by weightof a multicomponent superabsorbent fiber of claim
 42. 49. A method ofabsorbing an aqueous medium comprising contacting the medium with aplurality of fibers of claim
 42. 50. The method of claim 49 wherein theaqueous medium contains electroytes.
 51. A multicomponent superabsorbentfiber comprising: (a) a plurality of first fibers comprising an acidicresin, and (b) a plurality of second fibers comprising a basic resin,wherein the first and second fibers are admixed, then formed into theshape of a mat.
 52. The fiber of claim 51 wherein the mat is annealed ata temperature of about 65° C. to about 150° C. for about 20 minutes toabout 160 hours.
 53. The fiber of claim 51 wherein the mat retains itsstructural integrity after hydration with a liquid medium.
 54. Anarticle comprising a core containing about 1% to 100% by weight of amulticomponent superabsorbent fiber of claim
 51. 55. A method ofmanufacturing a multicomponent superabsorbent fiber comprising a corecomprising a poly(vinylamine) surrounded by a sheath comprising apoly(acrylic acid), said method comprising: (a) forming an aqueoussolution comprising an uncrosslinked poly(vinylamine) and about 0.001mol % to about 0.1 mol % of a crosslinking agent, (b) heating theaqueous solution of step (a) to lightly crosslink the uncrosslinkedpolyvinylamine and form a spinning dope, (c) introducing the spinningdope of step (b) into a coagulation bath containing about 0.1% to about2% by weight of a crosslinking agent dissolved in a nonsolvent forpoly(vinylamine) to form a filament of crosslinked poly(vinylamine), (d)directing the crosslinked poly(vinylamine) filament of step (c) from thecoagulation bath to a bath comprising poly(acrylic acid), about 0.5 toabout 5% by weight of a crosslinking agent, and a solvent, (e) passingthe crosslinked poly(vinylamine) through the bath of step (d) to form asheath of poly(acrylic acid) over the crosslinked poly(vinylamine)filament, (f) directing the filament from step (e) to a doping bathcontaining a curing catalyst, and (g) curing the filament from step (f)to provide the multicomponent superabsorbent fiber.
 56. The method ofclaim 55 wherein the crosslinked poly(vinylamine) dried after step (c)and prior to step (d).
 57. The method of claim 55 wherein the filamentformed in step (e) is dried prior to step (f).
 58. The method of claim55 wherein the crosslinking agent in step (a) comprising ethylene glycoldiglycidyl ether.
 59. The method of claim 55 wherein the crosslinkingagent in step (c) comprising ethylene glycol diglycidyl ether.
 60. Themethod of claim 55 wherein the crosslinking agent in step (d) comprisingethylene glycol diglycidyl ether.
 61. The method of claim 55 wherein thecuring catalyst of step (f) comprises triethylamine.
 62. The method ofclaim 55 wherein the filament of step (f) is cured in step (g) byheating for about 10 to about 60 minutes at about 60° C. to about 150°C.
 63. A method of manufacturing a multicomponent superabsorbentcomprising a mixed bed of fibers of an acidic resin and fibers of abasic resin, said method comprising: (a) admixing a plurality of acidicresin fibers and a plurality of basic resin fibers to form a fibermixture; (b) forming the fiber mixture into a mixed bed of apredetermined shape and thickness; and (c) annealing the mixed bed at atemperature of about 65° C. to about 150° C. for about 20 minutes toabout 16 hours.
 64. The method of claim 63 wherein the fiber mixture isformed into the shape of a diaper core.
 65. The fiber of claim 1 whereinthe fiber retains its structural integrity after hydration with a liquidmedium.